c.1300, from Old French chaeine "chain" (12c., Modern French chaîne), from Latin catena "chain" (source also of Spanish cadena, Italian catena), of unknown origin, perhaps from PIE root *kat- "to twist, twine" (cf. Latin cassis "hunting net, snare").
Figurative use from c.1600. As a type of ornament worn about the neck, from late 14c. Chain of stores is American English, 1846. Chain gang is from 1834; chain reaction is from 1916 in physics, specific nuclear physics sense is from 1938; chain mail first recorded 1822, in Scott, from mail (n.2). Before that, mail alone sufficed. Chain letter recorded from 1892; usually to raise money at first; decried from the start as a nuisance.
Chain smoker is attested from 1886, originally of Bismarck (who smoked cigars), thus probably a loan-translation of German Kettenraucher. Chain-smoking is from 1930.