Madcap means wildly reckless and funny with it. A madcap scheme, madcap adventures, a madcap comedy.
It is affectionate rather than critical, which is what separates it from reckless: a madcap scheme is one the speaker rather enjoys. It belongs to comedies and to descriptions of the young.
1adjectivemadcapWildly reckless and funny with it.
“They came up with a madcap plan to cycle across Africa on a tandem.”
madcap is a quality.
Mad plus cap, from cap in the old sense of the head.
The is derived from mad + cap. The is from an use of the noun.
Etymology from Wiktionary, CC BY-SA