Stir grain, removing article (4)
I believe the answer is:
whet
'stir' is the definition.
(I know that whet is a more specific form of stir)
'grain removing article' is the wordplay.
'grain' becomes 'wheat' (wheat is a type of cereal).
'removing' indicates named letters should be taken away.
'article' becomes 'a' (English indefinite article).
'wheat' with 'a' removed is 'WHET'.
(Other definitions for whet that I've seen before include "Excite" , "appetizer" , "Stimulate (appetite)" , "Make keen" , "Sharpen the blade of (a tool/weapon)" .)