Definition from Wiktionary, the free dictionary
plonker (plural plonkers)
- (UK, slang, mildly pejorative) A fool.
- (UK, slang) A penis.
- (UK, slang, dated) A man who sanctions sexual relationships between his girlfriend and his male friends.
- ^ BBC History- The WordhuntWordhunters noticed that the OED's earliest two quotations in their entry for 'plonker' were misplaced. In the original 1966 citation from All Neat in Black Stockings by J Gaskell, the word refers not to a 'foolish, inept or contemptible person', but to a wholly different sense of the word, meaning 'a man who sanctions sexual relationships between his girlfriend and his male friends'.