verb, let, let⋅ting, noun | 1. | to allow or permit: to let him escape. |
| 2. | to allow to pass, go, or come: to let us through. |
| 3. | to grant the occupancy or use of (land, buildings, rooms, space, etc., or movable property) for rent or hire (sometimes fol. by out). |
| 4. | to contract or assign for performance, usually under a contract: to let work to a carpenter. |
| 5. | to cause to; make: to let one know the truth. |
| 6. | (used in the imperative as an auxiliary expressive of a request, command, warning, suggestion, etc.): Let me see. Let us go. Just let them try it! |
| 7. | to admit of being rented or leased: The apartment lets for $100 per week. |
| 8. | British. a lease. |
| 9. | let down,
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| 10. | let in,
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| 11. | let off,
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| 12. | let on,
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| 13. | let out,
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| 14. | let up,
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| 15. | let up on, to treat less severely; be more lenient with: He refused to let up on the boy until his grades improved. |
| 16. | let alone. alone (def. 8). |
| 17. | let be,
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| 18. | let go. go (def. 82). |
| 19. | let someone have it, Informal. to attack or assault, as by striking, shooting, or rebuking: The gunman threatened to let the teller have it if he didn't move fast. |

let in on
Allow someone to know about or participate in something, as in I'm going to let you in on a little secret. This idiom was first recorded in 1904.