Meaning of “blue” - Learner’s Dictionary

blue

adjective uk us /bluː/
COLOUR

A1 being the same colour as the sky when there are no clouds:

a dark blue jacket
SAD informal

sad

SEX

about sex:

a blue joke/movie
→ See also black and blue , once in a blue moon

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