Heather's surviving without sex (4)
I believe the answer is:
ling
'heather's' is the definition.
(I've seen this before)
'surviving without sex' is the wordplay.
'surviving' becomes 'living' ('living' can be a synonym of 'surviving').
'without' suggests deleting specific letters.
'sex' becomes 'vi' ('sex' is Latin for 'six' or VI in Roman numerals).
'living' with 'vi' taken out is 'LING'.
(Other definitions for ling that I've seen before include "Slender food fish" , "Cod-like fish" , "Fish of the cod family" , "Common heather" , "Swimmer" .)