Start of crush — lose head for intimacy (9)
I believe the answer is:
closeness
'intimacy' is the definition.
(synonyms)
'start of crush lose head' is the wordplay.
'start of' suggests taking the first letters.
'head' becomes 'ness' (ness is a headland).
The first letter of 'crush' is 'c'.
'c'+'lose'+'ness'='CLOSENESS'
'for' is the link.
(Other definitions for closeness that I've seen before include "Proximity" , "sense of unity" , "State of being very near" .)