Keep detailed new free supplement (3,3)
I believe the answer is:
eke out
'supplement' is the definition.
(eking out is a kind of supplementing)
'keep detailed new free' is the wordplay.
'detailed' means to remove the last letter (the word must be end-less or 'de-tailed').
'new' is an anagram indicator.
'free' becomes 'out' (I've seen this before**).
'keep' with its last letter taken off is 'kee'.
'kee' is an anagram of 'eke'.
'eke'+'out'='EKE OUT'
(Other definitions for eke out that I've seen before include "Make (meagre supplies) last" , "Make last like scarce resources" , "Economise" , "Make something last by frugal use" , "Make it last, like a resource" .)