Idle maybe when entertained by a fellow in the USA (8)
I believe the answer is:
american
'in the usa' is the definition.
'idle maybe when entertained by a fellow' is the wordplay.
'idle maybe' becomes 'eric' (Eric Idle).
'when entertained by' means one lot of letters goes inside another.
'fellow' becomes 'man' (I've seen this before).
'a'+'man'='aman'
'eric' placed into 'aman' is 'AMERICAN'.
(Other definitions for american that I've seen before include "Eric, a man (anag.)" , "''The Quiet . . . . . . . .'' - Graham Greene" , "one like Garfield?" , "he's over the pond" , "The nationality is in camera, oddly" .)