From The Collaborative International Dictionary of English v.0.48 [gcide]:
Meth \Meth\, n.
See Meathe. [Obs.] --Chaucer.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
meth
n 1: an amphetamine derivative (trade name Methedrine) used in
the form of a crystalline hydrochloride; used as a
stimulant to the nervous system and as an appetite
suppressant [syn: methamphetamine, {methamphetamine
hydrochloride}, Methedrine, meth, deoxyephedrine,
chalk, chicken feed, crank, glass, ice, shabu,
trash]