Unlikely
Part of speech: adverb
Definition: In an improbable manner.
Part of speech: adjective
Definition: Not likely; improbable; not to be reasonably expected; as, an unlikely event; the thing you mention is very unlikely. Not holding out a prospect of success; likely to fail; unpromising; as, unlikely means.
Example sentence: Musicians now find themselves in the unlikely position of being legitimate. At least the IRS thinks so.
Implausible
Part of speech: adjective
Definition: Not plausible; unlikely; dubious.