suffragan
Concise Oxford English Dictionary © 2008 Oxford University Press:
suffragan /ˈsʌfrəg(ə)n/ (also suffragan bishop or bishop suffragan)
▶noun a bishop appointed to help a diocesan bishop.
■ a bishop in relation to his archbishop or metropolitan.
– origin ME: from Anglo-Norman Fr. and OFr., representing med. L. suffraganeus ‘assistant (bishop)’, from L. suffragium ‘suffrage’.
'suffragan' also found in these Oxford entries:

