Green’s Dictionary of Slang

an informer.

1554		Fox Martyrs n.p.: Accusers or peachers of others that were guiltless [F&H].
c.1698		B.E. Dict. Canting Crew n.p.: Whiddler, a Peacher (or rather Impeacher) of his Gang.
1926		Wood & Goddard Dict. Amer. Sl. 38: peach. To inform or tattle-tale upon. Hence, peacher.