Implacable rhymes with:
amicable, applicable, bankable, breakable, communicable, despicable, drinkable, eradicable, explicable, extricable, impeccable, impracticable, inapplicable, ineradicable, inextricable, irrevocable, likable, likeable, practicable, remarkable, revocable, talkable, unbreakable, unmistakable, unremarkable, unshakable, unshakeable, unsinkable, unspeakable, unthinkable, unworkable, workable
Implacable sounds like:
implausible, implausibly, impulsively, inapplicable, inflexible, inflexibly