lighten up

English

lighten up (third-person singular simple present lightens up, present participle lightening up, simple past and past participle lightened up)

(idiomatic, intransitive, transitive) To make (something) or to become less serious and more cheerful or casual; to relax.
Coordinate term: chill out

I wish he'd lighten up a bit and realize that we were only joking.

The mood at work has been tense, so he's looking for ways to lighten it up.
- 1983 August 6, Michael Bronski, “Gay Sensibility, Straight Imitation”, in Gay Community News, page 8:
  Sondheim's sense of life — which is pretty pessimistic (I don't think that anyone ever ends happily ever after in a Sondheim musical) — is brought through without trying to lighten it up.
- 2008, Adele, First Love:
  you lighten up my heart when I start to cry
(transitive) To lighten (something): to decrease its weight.
Near-synonym: slim down

He can't get any more power out of it [his drag racer], so now he's looking for ways to lighten it up.

to become less serious