1Lacking in some quality, attribute, or part necessary for full, efficient, and successful operation or action, or adequacy for the intended purpose; incomplete, defective, or flawed in some way; imperfect. Of something immaterial or abstract.
2Of a material thing.
3Of a person: not thoroughly accomplished or practised in a skill or pursuit; inexpert, unskilled.
Late Middle English (in an earlier sense). From un- + perfect, in early use partly after classical Latin imperfectus imperfect.