plunk

Onomatopoeic; the noun is attested earlier than the verb. Noun etymology 1 sense 3 (“dollar; large sum of money”) may refer to the sound of a coin hitting a surface. As regards verb etymology 1 sense 1.4 (“(transitive) to drop, set, or throw (something, or oneself) abruptly and/or heavily”) and etymology 1 sense 2.4 (“(intransitive) to drop, land, or set abruptly and/or heavily”), compare French plonquer (Picardy), a variant of plonger (“to plunge”).

Origin uncertain; possibly the same as plunk (etymology 1), or related to Dutch plenken (“(archaic) to wander around; (Limburg, archaic) to play truant”).