madcap

madcap \MAD-kap\, adjective:

1. wildly or heedlessly impulsive; reckless; rash: a madcap scheme.

noun:
1. a madcap person.

You can still see strong strains of formal qualities and madcap humor in his own work, which he began creating in 1971.

-- Claudia La Rocco, "Sights in New York Like No Others," The New York Times, Dec. 14, 2012

Slothrop recognizes him on sight, Judge Hardy's freckled madcap son, three-dimensional, flesh, in a tux and am-I-losing-my-mind face.

-- Thomas Pynchon, Gravity's Rainbow, 1995

Madcap is a portmanteau dated back to the late 1500s. The first part of this word comes from the Old High German gimeit, literally meaning "foolish" or "vain," and the second part takes a metaphorical spin on the the Late Latin cappa meaning "a hooded cloak."