Excellent American hotel down under (5)
I believe the answer is:
neath
'down under' is the definition.
'excellent american hotel' is the wordplay.
'excellent american' becomes 'neat' (US term for excellent).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'neat'+'h'='NEATH'
(Other definitions for neath that I've seen before include "Lower than - a town in West Glamorgan" , "not on top" , "Town near Swansea" , "Welsh rugby club" , "Welsh industrial town" .)