It supposedly means "a word that rhymes with nothing" or "a word that rhymes with month".
Purple rhymes with curple (1.the hindquarters or the rump of a horse, a strap under the girth of a horse's saddle to stop the saddle from kicking forward
2.(transf.) the rump, the posterior) , and
hirple (intransitive, Scottish, northern British) to walk with a limp, to drag a limb, to walk lamely; to move with a gait somewhere between walking and crawling.
Silver rhymes with
Wilver (a nickname) and
chilver (a ewe lamb).
Orange rhymes with
Blorenge (a mountain in Wales) and sporange (a sac where spores are made).