Crack female on island without a doubt (7)
I believe the answer is:
fissure
'crack' is the definition.
(I know that crack can be written as fissure)
'female on island without a doubt' is the wordplay.
'female' becomes 'f' (abbreviation).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'island' becomes 'is' (abbreviation).
'without a doubt' becomes 'sure' (I've seen this in another clue).
'f'+'is'+'sure'='FISSURE'
(Other definitions for fissure that I've seen before include "Split, crack" , "Split - cleavage" , "Crevice" , "Cleft" , "Long, narrow crack" .)