Green’s Dictionary of Slang

an informer.

1554		Fox Martyrs n.p.: Accusers or peachers of others that were guiltless [F&H].
1681		W. Stafford The tryal of William Viscount Stafford 110: This was three or four days before he begun to peach [...] That he should be a Peacher; and that there was a speech, how that he should have two hundred pounds for informing.
1697		E. Settle The world in the moon 38: Sir Dott. Why truly, Sir, if that False Peacher can Swear me or Lie me into a Halter, I shall be han’d and hang’d, and double hang’d.
1926		Wood & Goddard Dict. Amer. Sl. 38: peach. To inform or tattle-tale upon. Hence, peacher.