Synonyms: unconvincing, flimsy
Definition: not convincing
Usage: unconvincing argument; as unconvincing as a forced smile
Similar words: unpersuasive
Definition: not capable of persuading
Synonyms: improbable, unbelievable, unconvincing, unlikely
Definition: having a probability too low to inspire belief
Similar words: implausible
Definition: having a quality that provokes disbelief
Usage: gave the teacher an implausible excuse