Implausible rhymes with:
plausible, plausible, plausible, advisable, analyzable, disposable, divisible, excusable, exercisable, feasible, fusible, inadvisable, inexcusable, infeasible, invisible, plausible, realizable, recognizable, reusable, sizable, sizeable, unfeasible, unrecognizable, unusable, usable, visible
Implausible sounds like:
implacable, implausibly, impulsively, inapplicable, inflexible, inflexibly