For some time now, some of my on-line friends have advised me to provide a version of CassidySlangScam without the invective aimed at Cassidy and his supporters. In response to that advice, I am working on providing a glossary of the terms in Cassidy’s ludicrous book How The Irish Invented Slang with a short, simple and business-like explanation of why Cassidy’s version is wrong.
The late Daniel Cassidy, in his work of false etymologies, How The Irish Invented Slang, claimed that gauge or gage, a slang term for cannabis, derives from the Irish gaid.
Gaid is the plural of gad, which means a withe (a flexible stick) or else rope, usually rope in the form of a halter or noose (as in damhsa an ghaid, the gallows dance, dance on the end of a rope). Of course, rope is sometimes used as slang for cannabis, but not because it looks like rope. Ropes were made of hemp, which is cannabis. The word canvas also comes from cannabis. The chances of gaid being the origin of gage/gauge are next to zero, as withes and leaves of grass are very different things. Modern Irish speakers tend to call cannabis raithneach (fern) or féar (grass).
The mainstream dictionaries give various possible sources. One is a 17th. century term for a pipe, which seems quite unlikely to me. Another often-quoted idea is that this is a corruption of ganja, a West Indian term for dope derived from one of the Indian languages like Hindi or Gujarati. However, it seems that gage was also used as a term for a small quantity of something (possibly related to the word gauge meaning measure) and the term ‘a gage of tobacco’ is recorded from 1837. This last origin seems to be the strongest candidate.