Girl with love ensnaring American soldier slowly (6)
I believe the answer is:
adagio
'slowly' is the definition.
(musical term)
'girl with love ensnaring american soldier' is the wordplay.
'girl' becomes 'ada' (girl's name).
'with' says to put letters next to each other.
'love' becomes 'o' (love means zero in tennis).
'ensnaring' is an insertion indicator.
'american soldier' becomes 'GI' (informal term for a US soldier).
'ada'+'o'='adao'
'adao' placed around 'gi' is 'ADAGIO'.
(Other definitions for adagio that I've seen before include "leisurely movement" , "In slow time (mus.)" , "develops slowly" , "Leisurely, musically speaking" , "Musical composition to be played slowly and gracefully" .)