Is it ensure, insure, or assure?
"residue of fuel," 1690s, northern English dialect, perhaps a variant of Middle English colke "core, charcoal" (c.1400), itself possibly related to -colc, an Old English word for "pit," which perhaps would give it a sense of "what is left in the pit after a fire."
shortened form of cocaine, 1908, American English.
: coke peddlers/ coke sniffernoun
Coca-Cola, trademark name of a soft drink (1909+)