Relation: a funny tune inspiring one (6)
I believe the answer is:
auntie
'relation' is the definition.
(auntie is a kind of relation)
'a funny tune inspiring one' is the wordplay.
'funny' indicates anagramming the letters.
'inspiring' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'tune' anagrammed gives 'unte'.
'unte' placed around 'i' is 'untie'.
'a'+'untie'='AUNTIE'
(Other definitions for auntie that I've seen before include "woman in the family" , "Unite a strange relative" , "Close relative" , "Kinswoman" , "Relative (familiar)" .)