Unbelievable rhymes with:
believable, believable, believable, achievable, believable, conceivable, inconceivable, receivable, achievable, approvable, believable, conceivable, drivable, forgivable, immovable, inconceivable, livable, lovable, microwavable, movable, observable, provable, receivable, removable, solvable, survivable, unforgivable, unlivable, unsolvable
Unbelievable sounds like:
unavailable, unbelievably, unemployable, unflappable