Separate new unit constructed (7)
I believe the answer is:
untwine
'separate' is the definition.
(I've seen this before)
'new unit constructed' is the wordplay.
'constructed' indicates anagramming the letters.
'new'+'unit'='newunit'
'newunit' anagrammed gives 'UNTWINE'.
(Other definitions for untwine that I've seen before include "free?" , "Disentangle" , "Separate" , "Release" , "Unwind; untwist" .)