Meaning

noun a cheap wine of inferior quality

noun the noise of something dropping (as into liquid)

verb set (something or oneself) down with or as if with a noise

originFrom WWI military slang, derived by alteration of French vin blanc (“white wine”) by the law of Hobson-Jobson. Recorded earliest in the playful rhyming slang form plinketty-plonk. Possibly influenced by the sound of wine being poured into a glass.

Etymology from Wiktionary, CC BY-SA 3.0