It's a blemish in anyone's carpet (4)
I believe the answer is:
scar
'it's a blemish' is the definition.
(I've seen this before)
'in anyone's carpet' is the wordplay.
'in' indicates a hidden word.
'SCAR' is hidden in the letters of 'anyones carpet'.
(Other definitions for scar that I've seen before include "Evidence of an old wound" , "Mark of former injury" , "area of wound" , "Limestone cliff or outcrop" , "Permanent mark left by a wound" .)