Frothiness rhymes with:
cabiness, caviness, cleanliness, cloudiness, creepiness, friendliness, solitariness, steadiness, stinginess, storminess, unhappiness, wariness, worthiness
Frothiness sounds like:
farthing, farting, ferreting, fortune's, fortunes, forwarding, fourteens, freedman's, freedom's, freedoms, fretting, friedman's, fruiting