An American serving Dutch painter with dexterity (7)
I believe the answer is:
agilely
'an american serving dutch painter with dexterity' is the definition.
I can't judge whether this defines the answer.
'an american serving dutch painter' is the wordplay.
'an' becomes 'a'.
'american serving' becomes 'gi' (GI is a term for a US soldier).
'dutch painter' becomes 'lely' (17th-century artist Peter Lely).
'a'+'gi'+'lely'='AGILELY'
Can you help me to learn more?
(Another definition for agilely that I've seen is " With quickness and lightness".)