Place peg on couch (6)
I believe the answer is:
settee
'couch' is the definition.
(I know that settee is a type of couch)
'place peg on' is the wordplay.
'place' becomes 'set' (synonyms).
'peg' becomes 'tee' (tee is a kind of peg).
'on' says to put letters next to each other.
'set'+'tee'='SETTEE'
(Other definitions for settee that I've seen before include "Get a seat" , "chair" , "Item of furniture" , "Multiple seat" , "Intended recipient of my work, so to speak" .)