Leave cab seen in crash (7)
I believe the answer is:
absence
'leave' is the definition.
(thesaurus)
'cab seen in crash' is the wordplay.
'in crash' is an anagram indicator.
'cab'+'seen'='cabseen'
'cabseen' with letters rearranged gives 'ABSENCE'.
(Other definitions for absence that I've seen before include "It may make the heart grow fonder" , "What supposedly makes the heart grow fonder?" , "Abstraction" , "Cause of fonder heart?" , "It makes the heart grow fonder, they say" .)