Heartlessly xenophobic about a parting alien? Just so (5)
I believe the answer is:
exact
'just so' is the definition.
(I've seen this before)
'heartlessly xenophobic about a parting alien?' is the wordplay.
'heartlessly' suggests removing the centre.
'about' means one lot of letters goes inside another.
'parting' is an insertion indicator.
'alien?' becomes 'et' (extra terrestrial).
'xenophobic' with its middle taken out is 'xc'.
'xc' enclosing 'a' is 'xac'.
'xac' put within 'et' is 'EXACT'.
(Other definitions for exact that I've seen before include "Particular" , "Specific" , "without rounding" , "Spot-on" , "Explicit" .)