My wish turned out to be an odd idea (6)
I believe the answer is:
whimsy
'odd idea' is the definition.
'whimsy' can be an answer for 'idea' (whimsy is a kind of idea). I am unsure of the 'odd' bit.
'my wish turned out' is the wordplay.
'turned out' indicates an anagram.
'my'+'wish'='mywish'
'mywish' anagrammed gives 'WHIMSY'.
'to be an' is the link.
Can you help me to learn more?
(Other definitions for whimsy that I've seen before include "Fancy; notion" , "Capricious humour" , "Something fanciful" , "Capricious idea - sounds like Sayers' sleuth" , "Playfully quaint behaviour" .)