im·per·fect / imˈpərfikt/ • adj. 1. not perfect; faulty: an imperfect grasp of English. ∎  not fully formed or done; incomplete: imperfect census records smoke due to imperfect combustion.2. Gram. (of a tense) denoting a past action in progress but not completed at the time in question.3. Mus. (of a cadence) ending on the dominant chord.4. Law (of a gift, title, etc.) transferred without all the necessary conditions or requirements being met.• n. (the imperfect) Gram. the imperfect tense.DERIVATIVES: im·per·fect·ly adv.

imperfect not perfect XIV; (gram.) of a tense XVI. ME. inperfit — (O)F. imparfait; see IM-2, PERFECT.
So imperfection.