Peers squeal when reformed (6)
I believe the answer is:
equals
'peers' is the definition.
('equal' can be a synonym of 'peer')
'squeal when reformed' is the wordplay.
'when reformed' indicates anagramming the letters.
'squeal' anagrammed gives 'EQUALS'.
(Other definitions for equals that I've seen before include "Peer group" , "Persons of the same rank, for instance" , "They're at the same level" , "Those with the same status, rights, etc." , "Peers, matches" .)