a temporary lapse into foolishness, senseless behavior, folly, etc., especially during the summer:
His plan to become a beachcomber is midsummer madness.
foolish or extravagant behaviour, supposed to occur during the summer
noun 1. (functioning as singular or pl) another name for rose-root
noun the sun at noontime or midday; also written mid-sun
noun See midsun
[mid-teen] /ˈmɪdˈtin/ adjective 1. of, relating to, or characteristic of a person 15–17 years old: specializing in mid-teen clothes. noun 2. a person 15–17 years old: an ad campaign aimed at mid-teens. 3. mid-teens, numbers, amounts, ages, etc., midway between 13 and 19: He started at a salary in the mid-teens.