Meth

wiktionary

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Clipping of  methamphetamine. 

Clipping of  methadone. 

From meths or methylated spirits, as stereotypically drunk by tramps.

From metheglin, from Welsh meddyglyn, from meddyg(“medicinal”) (from Latin medicus) + llyn(“liquor”) (cognate with Irish lionn and Gaelic leann).

Clipping of  method, which see. 

etymonline

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meth (n.)

colloquial abbreviation of methedrine, attested from 1967.