Very stuck in one crack (5)
I believe the answer is:
solve
'crack' is the definition.
(thesaurus)
'very stuck in one' is the wordplay.
'very' becomes 'v' (abbreviation).
'stuck in' is an insertion indicator.
'one' becomes 'sole' ('sole' can be a synonym of 'one'**).
'v' placed inside 'sole' is 'SOLVE'.
(Other definitions for solve that I've seen before include "Loves (anag) - to find an answer" , "Unravel (a problem)" , "Settle" , "Get answer to (a clue)" , "Figure out the answer" .)