IPA: //ˈfuːlˌhɑːrdɪnəs//
KK: /ˈfuːlhɑːrdɪnəs/
The quality of being reckless or taking unnecessary risks without thinking about the consequences.
His foolhardiness led him to climb the mountain without proper gear.
Foolhardiness → It is formed from "fool" (from Old English *fola*, meaning a person lacking sense) and "hardy" (from Old French *hardi*, meaning bold or brave) with the suffix "-ness" (meaning the state of being). The word describes the state of being boldly foolish or recklessly brave.
Think of someone who is 'bold' ('hardy') but also 'lacking sense' ('fool') — that's what foolhardiness means, the state of being recklessly brave.