Without bells and whistles (5)
I believe the answer is:
plain
'without bells and whistles' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for plain that I've seen before include "Clear, candid" , "Unadorned on flat area" , "no oil painting features" , "Unflavoured" , "Flat land; unmarked" .)