Proportion for new share (6)
I believe the answer is:
ration
'share' is the definition.
(a ration is a share of a limited resource)
'proportion for new' is the wordplay.
'proportion' becomes 'ratio' (I've seen this before).
'for' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'ratio'+'n'='RATION'
(Other definitions for ration that I've seen before include "One's allotted portion" , "Restrict the supply of" , "A measured portion in times of scarcity" , "Fixed allotment" , "Limit supply in time of scarcity" .)