Sofa idler fetches to relax (12)
I believe the answer is:
chesterfield
'sofa' is the definition.
(chesterfield is a kind of sofa)
'idler fetches to relax' is the wordplay.
'to relax' indicates anagramming the letters (I've seen 'relaxing' mean this).
'idler'+'fetches'='idlerfetches'
'idlerfetches' is an anagram of 'CHESTERFIELD'.
(Other definitions for chesterfield that I've seen before include "Derby town?" , "Type of sofa - place in Derbyshire" , "Seat" , "Midlands town" , "He wrote, advising his son" .)