If all else fails lash out wildly (5)
I believe the answer is:
flail
'out wildly' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'if all else fails lash' is the wordplay.
'if all' anagrams to 'FLAIL'.
Though, I'm not clear how the anagram is indicated.
Can you help me to learn more?
(Other definitions for flail that I've seen before include "Wave about wildly" , "Weapon; swing wildly" , "thrash around" , "Thresher; wave helplessly about" , "Grain thresher" .)