One of a pair only changed at one point (5)
I believe the answer is:
nylon
'one of a pair' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'only changed at one point' is the wordplay.
'changed' indicates an anagram.
'at' says to put letters next to each other.
'one point' becomes 'n' (North).
'only' is an anagram of 'nylo'.
'nylo'+'n'='NYLON'
Can you help me to learn more?
(Other definitions for nylon that I've seen before include "Artificial cloth" , "Hose" , "Man-made fabric" , "Fabric (originally from New York and London)" , "Strong, resilient, synthetic fibre" .)