Green’s Dictionary of Slang

(W.I.) an obscenity, a swearword, a coarse, vulgar expression.

1989

C. Hyatt When Me Was A Boy 142: ‘Indecent language’ as them did call ‘bad wud’ a courthouse, was a serious offence [...] so although yuh coulda pop few ‘bluelight’ in the privacy of yuh own frien’ them, yuh never use none if girls aroun.