lucid interval. 1. A brief period during which an insane person regains sanity sufficient to have the legal capacity to contract and act on his or her own behalf. [Cases: Mental Health  3.1, 371; Wills  37. C.J.S. Insane Persons § 211; Wills § 9.] 2. A period during which a person has enough mental capacity to understand the concept of marriage and the duties and obligations it imposes. [Cases: Marriage  7. C.J.S. Marriage § 15.] 3. A period during which an otherwise incompetent person regains sufficient testamentary capacity to execute a valid will. — Also termed lucid moment.
[Blacks Law 8th]