Relaxed American guy (2,4)
I believe the answer is:
at ease
'relaxed' is the definition.
('at ease' can be similar in meaning to 'relaxed')
'american guy' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'guy' becomes 'tease' (I've seen this before).
'a'+'tease'='AT EASE'
(Other definitions for at ease that I've seen before include "Calm" , "Relaxing - that's a military order" , "Free from anxiety,in comfort" , "Comfortable" , "Free from anxiety" .)