n. The act of retaining or keeping back; restraint; reserve.n. The act of retaining or holding as one's own; continued possession or ownership.n. Continuance or perseverance, as in the use or practice of anything; preservation.n. The act of retaining or keeping in mind; especially, that activity of the mind by which it retains ideas; the retentive faculty: often used as synonymous with memory.n. Hence That which retains impressions, as a tablet.n. In medicine:n. The power of retaining, as in the stomach or bladder; inability to void or discharge: as, the retention of food or medicine by the stomach; retention of urine.n. Hence— A morbid accumulation of solid or liquid matter in vessels of the body or cavities intended to contain it only for a time.n. The state of being confined; custody; confinement.n. In Scots law, a lien; the right of withholding a debt or retaining property until a debt due to the person claiming this right is duly paid.n. Synonyms Reservation, preservation. See keep.