Tender name used for 'sweetheart' (10)
I believe the answer is:
endearment
'sweetheart' is the definition.
(sweetheart is a term of endearment)
'tender name used' is the wordplay.
'used' indicates an anagram.
'tender'+'name'='tendername'
'tendername' anagrammed gives 'ENDEARMENT'.
'for' acts as a link.
(Other definitions for endearment that I've seen before include "Affectionate utterance" , "Affectionate word" , "Affectionate term" , "Fondness" , "Word of affection" .)