Green’s Dictionary of Slang

peep n.³

[pron. of the two ‘P’s in PCP]

(drugs) phencyclidine.

1979		H. Feldman et al. Angel Dust 74: Phencyclidine is available today under a wide array of street names: T, P, tish or titch, peep.
2001		ONDCP Street Terms 16: Peep — PCP.