Peer is said to be childless (6)
I believe the answer is:
barren
'be childless' is the definition.
(synonyms)
'peer is said' is the wordplay.
'peer' becomes 'baron' (baron is a kind of peer).
'is said' shows a homophone (sound like).
'baron' is a homophone of 'BARREN'.
'to' is the link.
(Other definitions for barren that I've seen before include "Sterile" , "Unable to reproduce, infertile" , "Infertile, unproductive" , "Unproductive of life" , "Incapable of sustaining life" .)