Rapidity rhymes with:
acidity, fluidity, humidity, liquidity, morbidity, rigidity, solidity, superfluidity, timidity, turbidity, validity
Rapidity sounds like:
rabbit, rabbitt, rabid, rabideau, raffetto, raffety, raft, rafted, raped, rapid, rapped, rapt, rarefied, raved, reaped, rebate, rebated, rebid, rebuffed, rebut, rebutted, refaat, reffett, reffitt, refit, refitted, refute, refuted, repaid, repeat, repeated, repetti, repetto, repudiate, repudiated, repute, reputed, revette, reviewed, revived, revved, ribaudo, ribbed, ribbit, riffed, rift, ripped, rippetoe, rivet, riveted, rivett, rivette, robbed, robed, robideau, robot, roofed, roped, rovito, rowboat, rubbed, rubout, rufty