Why is the ninth month called September?
c.1300, common European bird (Garrulus glandarinus), from Old North French gai, Old French jai "magpie, jay," from Late Latin gaius "a jay," probably echoic and supposedly influenced by Latin Gaius, a common Roman proper name. For other bird names from proper names, cf. martin and parrot. Applied to the North American blue jay (Cyanocitta cristata) from 1709. Applied to humans in sense of "impertinent chatterer, flashy dresser" from 1620s.
"fourth-rate, worthless" (e.g. a jay town), 1888, American English, apparently from some disparaging sense of jay (n.). Perhaps from a decaying or ironical use of jay "flashy dresser."
[fr the raucous bird]
Marijuana or a marijuana cigarette; j: Let's do up a jay and truck on down to the libo (1960s+ Narcotics)