Are not, I hear, with a relative? (4)
I believe the answer is:
aunt
'a relative?' is the definition.
(aunt is a kind of relative)
'are not i hear' is the wordplay.
'are' becomes 'a' (short for 'are', historical unit of measurement).
'not' becomes 'n't' (synonyms).
'i hear' indicates a 'sounds like' (homophone) clue.
'a'+'nt'='ant'
'ant' is a homophone of 'AUNT'.
'with' is the link.
(Other definitions for aunt that I've seen before include "Family relative" , "Parent's sister" , "Female relative" , "Tuna (anag.)" , "Uncle's wife" .)