Fit one new counter (7)
I believe the answer is:
install
'fit' is the definition.
(thesaurus)
'one new counter' is the wordplay.
'one new' becomes 'in' (I've seen this in other clues).
'counter' becomes 'stall' (as in a stall or counter at a market).
'in'+'stall'='INSTALL'
(Other definitions for install that I've seen before include "Put into position, ready for use" , "put in office" , "Lodge" , "Place in position, establish" , "Fix (equipment) in position" .)