Definition - What does Reefer mean?
Reefer is a cannabis slang term used to refer to either marijuana plants, or a marijuana cigarette, or joint, either one that's rolled by hand or one that has been machine rolled.
While not an antiquated or unused word, reefer's predominance in English slang as a term for marijuana has waned and it is not as widely used in the 21st century as it was previously.
MaximumYield explains Reefer
In pop-culture, the word reefer is largely associated with the early 20th century anti-marijuana propaganda film Reefer Madness, which purported (incorrectly and now seen as humorously) that the use of marijuana would lead to the commissions of violent crimes, cause insanity, and be responsible for numerous other forms of societal deviance.
The word reefer is generally used interchangeably with such slang terms as “weed”, “pot”, “Mary Jane” and hundreds of other terms used to refer to cannabis and cannabis use, including ones broadly recognized and ones that are only regionally used.
There are two possible etymological origins of the word reefer. The first relating to a rolled reef sail on a boat, and the plausibility that its appearance may be comparable to that of a marijuana cigarette. Another possibility is its similarity to the Spanish word of Mexican origin, “grifo” meaning an addict of or smoker of marijuana.