Kindergarten subject (4)
I believe the answer is:
abcs
'kindergarten subject' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abcs that I've seen before include "guides ..." , "Know these to be well versed - alphabetically?" , "Know these letters to be well informed" , "12 [THINGS EASY]" .)