Plethora rhymes with:
eleuthera, acampora, acura, agora, amphora, anaphora, andera, ankara, aventura, bachera, barbara, camera, cetera, cholera, corpora, deborah, diaspora, eleuthera, etc, etcetera, genera, imbera, kuchera, lenora, maquiladora, reitera, samara, tempera, theora, vanora
Plethora sounds like:
paltry, pelletier, peltier, pfleiderer, plater, platter, plotter, polder, polidori, polidoro, polluter, poulter, poultry