Green’s Dictionary of Slang

1. a drug addict; a drug user.

1942		Berrey & Van den Bark Amer. Thes. Sl.
1953		Anslinger & Tompkins Traffic In Narcotics 307: dip. A drug addict.

2. a dose or portion of a drug.

1959

J.E. Schmidt Narcotics Lingo and Lore.

3. crack cocaine.

2001		ONDCP Street Terms 7: Dip — Crack Cocaine.
2012		W.D. Myers All the Right Stuff 123: [T]hey start self-medicating—smoking dip and snorting girl.

4. a cigarette dipped into sherm n., i.e. formaldehyde.

2000

in W. Shaw Westsiders 304: We gon’ smoke a dip — sherm stick.

5. (N.Z. drugs/prison) a tablet of LSD.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 56/2: dip (also dipper or double dip) n. 1 an LSD tab.