let in

2 meanings

Meanings
  1. 1 tell someone a secret or private information B2
  2. 2 allow someone or something to come inside A2
1 let sb in on sth

tell someone a secret or private information

B2

What does "let in" mean in this sense?

To 'let someone in on' something means to deliberately share a secret, plan, or piece of exclusive knowledge with them. The key idea is inclusion — you are choosing to bring someone into a small group of people who know something others don't. This gives the phrase a slightly conspiratorial or generous feeling, as if you are doing someone a favour by trusting them with the information. It is most common in casual, spoken English — you would use it with friends, family, or close colleagues, not in a formal report or professional email. Unlike simply 'telling someone a secret', this phrase emphasises that the other person is being let into an inner circle of knowledge.

Examples

How to use it

let + person + in on + secret/information

This is the standard, essential structure — the person being included always comes before 'in on', and the secret or information follows 'on'.

I'll let you in on a little secret if you promise to keep quiet about it.

let + person + in on + it/this/that

When the secret or information is already understood from context, a pronoun can replace the noun after 'on'.

Everyone else already knew — I can't believe they didn't let me in on it sooner.

refuse/decide/agree + to let + person + in on + something

This verb often follows another verb that expresses a decision or willingness, showing whether someone chooses to share the information or not.

She decided to let her sister in on the surprise before anyone else found out.

finally/eventually + let + person + in on + something

Adverbs like 'finally' or 'eventually' are very common here, since sharing the secret is often something that happens after a period of waiting or hesitation.

After weeks of hinting, he finally let us in on the details of his new project.

be let in on + something (passive)

A passive construction is possible, though not very common — it shifts focus to the person who receives the information rather than the one who shares it.

She was let in on the plan just hours before it was announced to everyone else.

Common Collocations

let someone in on a secretlet someone in on the jokelet someone in on the planlet someone in on the detailslet someone in on what's happeninglet someone in on the truth

Common Mistakes

Missing 'on'

The most common mistake is dropping 'on' and saying 'let me in the secret'. This is always wrong — you must include 'on' before the information noun or pronoun.

✗ Can you let me in the secret?
✓ Can you let me in on the secret?
Confusing with 'let in' (physical meaning)

Without 'on' and an information noun, 'let someone in' means to allow someone to enter a place — a completely different meaning. Always include 'on + [information]' to make the secret-sharing sense clear.

✗ She let us in before the meeting started. (could mean physical entry)
✓ She let us in on what was going to happen before the meeting started.
Confusing with 'let on'

'Let on' means to reveal what you already know, often reluctantly or accidentally. 'Let someone in on' means to deliberately include another person in a secret. They are not interchangeable.

✗ He didn't want to let on his colleagues the truth about the deal.
✓ He didn't want to let his colleagues in on the truth about the deal.

Usage

This phrasal verb is informal and mostly spoken. It always follows the pattern 'let [person] in on [something]' — never drop the 'on'.

2 let sb/sth in

allow someone or something to come inside

A2

Sense 2: What does "let sb/sth in" mean?

To let someone in means to allow them to enter a place, such as a house, a room, or a building. You might let in a friend who knocks at your door, or a security guard might let visitors into an office. This phrasal verb also works with animals — for example, letting the dog or cat inside — and with non-human things like light, air, or rain that pass through a window or gap. It is a very common, everyday expression that works in all kinds of situations, from casual home life to more formal settings like shops or venues.

Examples

How to use it

let + person/animal + in

The most common pattern, where a person or animal is allowed to enter. The object goes between 'let' and 'in'.

There's someone at the door — can you let them in?

let + pronoun + in

When the object is a pronoun (him, her, them, it), it must always go between 'let' and 'in'.

The cat was scratching at the door, so I let her in.

let in + noun phrase

With longer noun phrases, the object can follow 'in' instead of being placed in the middle.

Please don't let in any visitors without a pass.

let in + thing (light, air, rain, cold)

Used when something non-human, like light or cold air, enters through an opening.

Open the window a little — it will let in some fresh air.

be let in

The passive form is used when the focus is on who was or wasn't allowed to enter.

He wasn't let in because he had forgotten his membership card.

Common Collocations

let the dog inlet someone inlet the light inlet guests inlet the cold inlet strangers in

Common Mistakes

Pronoun placement

When the object is a pronoun like 'him', 'her', 'them', or 'it', it must go between 'let' and 'in'. Putting the pronoun after 'in' is not correct in English.

✗ She let in them after they knocked.
✓ She let them in after they knocked.
Confusing 'let in' with 'let in on'

'Let in' means to allow someone to physically enter a place. 'Let in on' means to share a secret with someone. If you see 'on' after 'in', the meaning is completely different.

✗ He finally let me in the secret.
✓ He finally let me in on the secret. / He finally let me in — I had been waiting outside!

Usage

This phrasal verb is neutral and works in all everyday situations. It also describes letting non-human things like light, air, or rain enter — not just people or animals.

Frequently Asked Questions

Can I say 'I am letting you in on a secret' in the present continuous?

It's better to avoid it — the present continuous sounds unnatural with this phrasal verb. Native speakers would more likely say 'I'll let you in on a secret' or use a simple tense instead.

Does 'let someone in on' always involve an actual secret?

Not necessarily — it just needs to be information that not everyone knows. You can let someone in on a plan, a joke, the details of a surprise, or something that's been kept quiet. The key is that it feels like exclusive or insider knowledge.

Can I use 'let someone in on' in an email or at work?

It's fine in a casual email to a colleague or friend, but it would sound too informal in a formal business document or professional report. Stick to relaxed, conversational contexts when using this phrase.

What's the difference between 'let someone in on something' and 'fill someone in'?

'Fill someone in' usually means catching a person up on information they missed — like updating a colleague on what happened in a meeting. 'Let someone in on' suggests you are sharing something secret or exclusive, where inclusion feels deliberate and special.

Do I always need to say what the secret is, or can I leave it vague?

You can keep it vague using words like 'something' or 'it' — for example, 'I'll let you in on something later' or 'she let me in on it'. As long as the context makes the information understood, you don't need to spell it out.

Can 'let in' be used for things like light or rain, not just people?

Yes! It is very natural to use 'let in' for non-human things that enter through a gap or opening. For example, 'The broken window lets in the rain' or 'Pull back the curtains to let in some light.' This is a common and everyday use of the phrasal verb.

Does 'let in' have more than one meaning?

Yes. The most common meaning is to allow someone or something to physically enter a place. There is also a second meaning — 'let someone in on something' — which means to share a secret or private information with them. You can tell the difference because the secret-sharing sense always has 'on' after 'in' and is followed by something abstract like a plan or a secret.

What is the difference between 'let in' and 'let into'?

'Let in' is used when the place is already clear from the context, or when you are speaking generally. 'Let into' is followed directly by a specific place, for example 'let into the building' or 'let into the room'. Both are correct, but 'let into' names the destination more explicitly.

Can I use 'let in' in the passive, like 'she was let in'?

Yes, the passive form is perfectly natural. You can say things like 'He was let in through the back door' or 'No one was let in without a ticket.' The passive is useful when you want to focus on the person entering rather than the person allowing them in.

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