Green’s Dictionary of Slang

tish n.

also titch
[var. on tic n.2 ]

(drugs) phencyclidine.

[US]H. Feldman et al. Angel Dust 74: Phencyclidine is available today under a wide array of street names: T, P, tish or titch.
[US]ONDCP Street Terms 21: Tish — PCP. [...] Titch — PCP.