Spin dry tops for instance, each plain (7)
I believe the answer is:
prairie
'plain' is the definition.
(type of plain)
'spin dry tops for instance each' is the wordplay.
'spin' becomes 'PR' (public relations).
'dry' becomes 'air' (airing is a kind of drying).
'tops for' indicates taking the first letters (in a down clue, the tops are the top letters).
The initial letters of 'instance each' is 'ie'.
'pr'+'air'+'ie'='PRAIRIE'
(Other definitions for prairie that I've seen before include "Large treeless tract of grassland" , "Open grassland of North America" , "Large tract of grassland in N America" , "Continental grassland of N America" , "this oyster produces an egg" .)