Estimate about rug (3)
I believe the answer is:
mat
'rug' is the definition.
(both are floor coverings)
'estimate about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'MAT' is hidden within 'estimate'.
(Other definitions for mat that I've seen before include "Opening of good book" , "Small protective floor-covering" , "Dull, rug" , "Small carpet" , "Rug; without a shine" .)