implausible
1. [ adjective ] having a quality that provokes disbelief
Examples:

"gave the teacher an implausible excuse"

Related terms: plausible improbable incredible
2. [ adjective ] highly imaginative but unlikely
Synonyms: farfetched
Examples:

"a farfetched excuse" "an implausible explanation"

Related terms: unlikely
Similar spelling:   implausibly
  implacable
  implausibility
  implosion