unbelievablest

Adjective

unbelievable (comparative more unbelievable or (rare, nonstandard) unbelievabler, superlative most unbelievable or (rare, nonstandard) unbelievablest)

1. (literally) Not to be believed.
   • ‘Come on, girls,’ said Steve, ‘be honest, we won.’ / ‘Yeah,’ said Raymond, ‘we let you off because you’re girls.’ / ‘You’re unbelievable,’ said Liz. / ‘Well, if we’re unbelievable,’ said Steve, ‘then you’re unbelievabler.’1996, Colin Thompson, “Four Pigeons”, in Venus the Caterpillar and Further Wild Stories, London: Hodder Children’s Books, →ISBN, page 24

   Synonyms:

   beyond belief, incredible, noncredible

   Antonyms:

   believable, credible

2. (figuratively) Amazing, astonishing; so surprising that one is almost, or figuratively, unable to believe.
   • The most unbelievable thing happened to me today!

   Synonyms:

   incredible

3. Implausible or improbable.
   • His excuse seems rather unbelievable.

   Synonyms:

   improbable, infeasible, unlikely

   Antonyms:

   feasible, likely, plausible, probable