A cigarette consisting solely of the wicked weed. This, to my
understanding, distinguishes it from a 'joint,' which is traditionally rolled with a combination of tobacco and marijuana. However, the american tradition of smot-poking consist mostly of rolling marijuana-only cigarettes, therefore the words 'reefer' and 'joint' are interchangeable.
The word 'reefer' probably comes from sailing terminoligy: when you 'reefer' the sails you narrow them and roll them up, and considering that modern marijuana use
originated in the lower class, it's easy to see how a poor deckhand would associate this with the way he rolled his
marijuana cigarette.