Less than a clear field? (3)
I believe the answer is:
lea
'field?' is the definition.
(lea can mean a meadow or field of grass)
'less than a clear' is the wordplay.
'less' indicates a hidden word (the clue less some of the letters in it).
'LEA' is hidden in the letters of 'than clear'.
(Other definitions for lea that I've seen before include "authority for teachers" , "Field" , "'The lowing herd wind slowly o'er the . . .'" , "Poetically, a piece of meadow or pasture" , "Open area of grassy or arable land" .)