Almost the ultimate check carpet (3)
I believe the answer is:
mat
'carpet' is the definition.
(a mat is a floor covering)
'almost the ultimate check' is the wordplay.
'check' says the answer is hidden in the clue (I've seen 'checks' mean this (check can mean to curb or restrain)).
'MAT' can be found hidden inside 'almost ultimate'.
(Other definitions for mat that I've seen before include "coaster" , "knot" , "Small rug" , "Floor-pad" , "Tangle" .)