: any of various small, often brightly colored tropical fish (genus Poecilia) that are live-bearers found in fresh, brackish, or salt water and include several that are highly valued as aquarium fishes
: the illicit drug ecstasy (see ecstasysense 2) especially when in a powdered or crystalline form contained in a capsule
Boston Police said Thursday that a dangerously pure form of the drug ecstasy, known as Molly, appeared to be a factor in the mass illnesses the night before at TD Garden, where more than 80 young people attending an electronic dance music concert became sick … Evan Allen
Experts say Molly, though often touted as pure, is often mixed with other drugs and ingredients, perhaps even more than the Ecstasy of yesteryear. Helena Oliveiro
Word History
Etymology
Noun (1)
by shortening from New Latin Mollienisia, former genus name, from Comte François N. Mollien †1850 French statesman
Noun (2)
of obscure origin
Note: Perhaps from the given name Molly, but if so the motivation is unclear. In the United Kingdom a parallel name for a powder or capsule form of the drug is mandy, which bears somewhat greater resemblance to the initialism MDMA. There appears to be no compelling reason to take molly as a clipping of molecular. Note that black molly was a jargon term for amphetamine capsules in the 1970's (see entry in The New Partridge Dictionary of Slang and Unconventional English [Routledge, 2005]).