American plain (7)
I believe the answer is:
prairie
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">american plain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for prairie that I've seen before include "American plain" , "-- Dog; -- oyster" , "Open grassland in the USA" , "North American grassland" , "Wide grassy plain" .)