billy

Of obscure origin. Perhaps a variant of bully (“companion, mate, comrade”). Compare Scots billie (“a comrade; companion”). Compare also Middle Low German billig (“equitable, reasonable, lawful, fitting, according to natural law, just”).

Uncertain, but probably extracted from Scots billypot (“a type of cooking pot”), perhaps originally from the name Billy, a diminutive of William.

The condom sense from the E-Rotic song Willy, Use a Billy... Boy, referring in turn to Billy Boy, a German brand of condoms.