Trouble about a US soldier being slow (6)
I believe the answer is:
adagio
'slow' is the definition.
(similar in meaning)
'trouble about a us soldier' is the wordplay.
'trouble' becomes 'ado' (both can mean bother or commotion).
'about' means one lot of letters goes inside another.
'us soldier' becomes 'GI' (informal term for a US soldier).
'a'+'gi'='agi'
'ado' placed around 'agi' is 'ADAGIO'.
'being' acts as a link.
(Other definitions for adagio that I've seen before include "Slow movement (music)" , "Slow musical passage" , "(A movement) to be played slowly" , "leisurely movement" , "going slowly in work" .)