Five, four or three — or two, but not one (3)
I believe the answer is:
par
'five four or three' is the definition.
(usual par numbers on golf holes)
'two but not one' is the wordplay.
'two' becomes 'pair' (pair is a kind of two).
'but not' is a deletion indicator.
'one' becomes 'i' (Roman numeral).
'pair' with 'i' removed is 'PAR'.
'or' is the link.
(Other definitions for par that I've seen before include "Expected number of strokes for hole (golf)" , "Standard amount" , "Median" , "Accepted level" , "Regular score" .)