We're not exactly sure how long ago the term weed first started being used to refer to cannabis (marijuana, herb, hemp, etc.), but we do know that Shakespeare wrote about "finding invention in the noted weed" in his sonnets, written in the late 1600's.
We named our book The Newbie's Guide To Medicinal Cannabis and not The Newbie's Guide To Medicinal Weed (or Medical Weed) because (a) Cannabis is the older and more botanically & historically accurate term, and (b) while the term weed isn't quite pejorative, it's not specific either and could be open to interpretation, as "weed" (in other contexts) can refer to any plant not just cannabis. We also don't like the term weed because of the negative connotation of the "garden variety" definition of weed, i.e. a plant that's not wanted where it's currently growing. We at The Dà Má Collective prefer the term cannabis over weed, but we like the term weed better than marijuana (while weed isn't as specific of a term as it could be, it doesn't have the racially pejorative overtones that marijuana does either). Plus weed is the term Shakespeare uses :-)
This page is part of a larger collection on Words/Terms for Cannabis, which is an extract/preview (dab? :) from The Newbie's Guide To Medicinal Cannabis by The Dà Má Collective 大 麻