Love uncommonly tender man, engaging European (10)
I believe the answer is:
endearment
'love' is the definition.
'uncommonly tender man engaging european' is the wordplay.
'uncommonly' indicates anagramming the letters.
'engaging' indicates putting letters inside.
'european' becomes 'e' (abbreviation e.g. EU).
'tender'+'man'='tenderman'
'tenderman' is an anagram of 'endarment'.
'endarment' enclosing 'e' is 'ENDEARMENT'.
(Other definitions for endearment that I've seen before include "Term of affection" , "Affectionate term" , "Pet name" , "sign of affection" , "Fondness" .)