Unwisely takes a bet (5)
I believe the answer is:
stake
'a bet' is the definition.
(I know that bet can be written as stake)
'unwisely takes' is the wordplay.
'unwisely' indicates an anagram.
'takes' with letters rearranged gives 'STAKE'.
(Other definitions for stake that I've seen before include "Sharpened post; sum bet" , "that's used in punt" , "Money gambled" , "Investment" , "Ante, bet" .)