plonk: English has two distinct words plonk. The one that means ‘put down firmly and heavily’ [19] was no doubt originally simply an imitation of the sound made by the action (alternative realizations of which are plank and plunk). The other, ‘cheap bog-standard wine’ [20], appears to have originated among Australian troops serving in France during World War I, which lends credence to the supposition that it was based on a French original – generally supposed to be vin blanc ‘white wine’.
It is true that not until the 1930s do we have any written evidence of plonk in this sense, nor of its possible precursor plinkety-plonk (which could have been a comical rhyming variation on vin blanc, and which also produced the shorter-lived spin-off plink in the same sense), and that nowadays the term seems to be applied mainly to red wine rather than white. Nevertheless, there are relevant records of Great-War-period puns (for example von blink as a ‘humorous corruption’ of vin blanc), and the explanation has an air of plausibility.
