Peer is number five to start (8)
I believe the answer is:
viscount
'peer' is the definition.
(viscount is a kind of peer)
'is number five to start' is the wordplay.
'number' becomes 'count' (count is a kind of number**).
'five' becomes 'v' (roman numeral).
'to start' is a charade indicator (letters next to each other).
'is'+'count'='iscount'
'iscount' after 'v' is 'VISCOUNT'.
(Other definitions for viscount that I've seen before include "Minor peer" , "Lord" , "Nobleman" , "plane" , "British noble" .)