The story
The noun is derived from mad + cap (“(informal) head”). The adjective is from an attributive use of the noun.
First known use, by meaning
- from late 16th c. An insane person; a lunatic.
Etymology from Wiktionary, CC BY-SA 4.0.
madcap
mad·capToday it means: A person who acts in a capricious, impulsive, or reckless manner. Full definition →
First used late 16th c.