Resident American consumed by frontier (7)
I believe the answer is:
boarder
'resident' is the definition.
(someone boarding in a particular residence)
'american consumed by frontier' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'consumed by' means one lot of letters goes inside another.
'frontier' becomes 'border' (I've seen this before).
'a' placed into 'border' is 'BOARDER'.
(Other definitions for boarder that I've seen before include "pirate?" , "Live-in school pupil" , "Resident pupil" , "Schoolchild perhaps" , "one that's getting on plane" .)