imperturbablea GRE synonym for 'unshakeable' meaning unable to be upset or agitated; supremely collectedThe imperturbable surgeon continued the operation despite the power flicker.NoteThe imperturbable surgeon continued the operation despite the power flicker.Elon.io is an online learning platformWe have an entire course teaching GRE Verbal — Essential Vocabulary grammar and vocabulary.Start learning GRE Verbal — Essential Vocabulary now