the.com/roach

means A cockroach — the hardy, flat-bodied insect that scuttles through kitchens at night and survives almost anything you throw at it; also slang for the butt end of a smoked joint.

from English 'roach' is a clipped, altered form of 'cockroach,' which itself came from Spanish 'cucaracha' in the 1600s — English speakers mangled the unfamiliar word, splitting off a 'cock' they thought they heard at the front, and later the 'cock' got dropped, especially in American slang, leaving plain 'roach.' The joint-related sense (the leftover stub) is 20th-century slang, likely because the small dark stub resembled the bug — a visual pun rather than a shared root.