The word ‘let‘ can mean many different things. As a verb, the meaning is to allow.
For example:
- My mum lets me stay up until 11 at the weekend. (allow)
Let is an irregular verb. The past tense is let and the past participle is let.
idioms list with ‘let’
- don’t let the bed bugs bite – wishing someone a good night’s sleep
e.g. It’s past your bed time, go upstairs now. Don’t let the bed bugs bite. - don’t let the grass grow under one’s feet – hurry, act now, don’t wait
e.g. Brian is a useless employee. We’ve lost so much business by him letting the grass grow. - let nature take its course – allow events to develop naturally, don’t interfere
e.g. I’ve bandaged the baby owl’s leg, now I have to let nature take its course. - let one’s hair down – relax and have fun
e.g. The kids are with grandad so I will let my hair down this weekend. - let someone stew – allow someone to worry/be fearful about something they have done
e.g. My girlfriend hasn’t messaged me all day. She’s letting me stew as I forgot her birthday. - let the cat out of the bag – reveal the secret
e.g. We’re throwing a surprise party for my parents, don’t let the cat out of the bag.
let the side down – disappoint your friends/family/colleagues
e.g. I want you all playing your best. If you let the side down, you’re out of the team.
Let’s see these idioms with pictures and meaning using real-life scenarios.

Psst…
Hey, did you know the verb ‘let’ has many phrasal verbs. Since you like idioms and phrases, you obviously want to improve your fluency and speak like a native.
Am I right?
I thought you might like to learn the phrasal verbs with ‘let’ too. They are very common in informal English and great to know/be able to understand if you happen to be speaking to a native. We use them all the time, like literally ALL the time.