Meaning of “sober” - Learner’s Dictionary

sober

adjective uk us /ˈsəʊbər/
NOT DRUNK

Someone who is sober is not drunk.

SERIOUS

Someone who is sober is serious and thinks a lot:

He was in a sober mood.
NOT BRIGHT UK

Clothes or colours that are sober are plain and not bright:

a sober, grey dress
soberly adverb

(Definition of “sober” from the Cambridge Learner’s Dictionary © Cambridge University Press)