Place American on mountain pass, returning (5)
I believe the answer is:
locus
'place' is the definition.
('place' in Latin)
'american on mountain pass returning' is the wordplay.
'american' becomes 'us' (abbreviation for United States).
'on' says to put letters next to each other.
'mountain pass' becomes 'col' (col is a kind of mountain pass).
'returning' says the letters should be written in reverse.
'col' in reverse letter order is 'loc'.
'us' put after 'loc' is 'LOCUS'.
(Other definitions for locus that I've seen before include "line" , "Position, point, place" , "Particular place something is found" , "Particular position (of something)" , "place in court matters" .)