Chin-wagging, to an extent (4)
I believe the answer is:
inch
'an extent' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'chin-wagging' is the wordplay.
'wagging' is an anagram indicator (letters swing or wag around).
'chin' anagrammed gives 'INCH'.
'to' is the link.
Can you help me to learn more?
(Other definitions for inch that I've seen before include "Move very slowly - a very short distance" , "Advance slowly" , "Part of a foot" , "Small measurement unit of distance" , "Move in tiny increments" .)