Definition of "blue"
blue1
adjective
comparative bluer or more blue, superlative bluest or most blue
(informal) Depressed, melancholic, sad.
(archaic, of women) literary; bluestockinged.
(informal) Risqué; obscene; profane; pornographic.
(slang, dated) Drunk.
noun
countable and uncountable, plural blues
(countable and uncountable) The colour of the clear sky or the deep sea, between green and purple in the visible spectrum, and one of the primary additive colours for transmitted light; the colour obtained by subtracting red and green from white light using magenta and cyan filters; or any colour resembling this.
(slang) A member of law enforcement.
(now historical) A bluestocking.
(Britain) A type of firecracker.
verb
third-person singular simple present blues, present participle blueing or bluing, simple past and past participle blued