IPA: //ˈfuːlˌhɑːrdɪli//
KK: /ˈfuːlˌhɑːrdɪli/
In a way that shows a lack of care or thought for the consequences of actions; recklessly or rashly.
He foolhardily jumped into the river without checking the depth.
Foolhardily → 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 adverbial suffix "-ly" (meaning in a manner). The word describes acting in a bold or brave manner without sense or wisdom, often recklessly.
Think of someone who is 'bold' ('hardy') but lacks 'sense' ('fool') — that's why foolhardily means acting recklessly.
No commonly confused words.