immaculateyoudaoicibaDictYouDict
immaculate: [15] A macula in Latin was a ‘spot’ or ‘stain’ (as well as a ‘hole in a net’, which gave English the mail of chain mail). Hence anything that was immaculātus (an adjective formed with the negative prefix in-) was ‘spotless’ – ‘perfect’.
=> chainmail
chain (n.)youdaoicibaDictYouDict
c. 1300, from Old French chaeine "chain" (12c., Modern French chaîne), from Latin catena "chain" (source also of Spanish cadena, Italian catena), which is of unknown origin, perhaps from PIE root *kat- "to twist, twine" (cognates: 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.
Nine out of every ten givers are reluctant and unwilling, and are coerced into giving through the awful fear of "breaking the chain," so that the spirit of charity is woefully absent. ["St. Nicholas" magazine, vol. XXVI, April 1899]
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.
stuff (n.)youdaoicibaDictYouDict
early 14c., "quilted material worn under chain mail," from Old French estoffe "quilted material, furniture, provisions" (Modern French étoffe), from estoffer "to equip or stock," which according to French sources is from Old High German stopfon "to plug, stuff," or from a related Frankish word (see stop (v.)), but OED has "strong objections" to this.

Sense extended to material for working with in various trades (c. 1400), then "matter of an unspecified kind" (1570s). Meaning "narcotic, dope, drug" is attested from 1929. To know (one's) stuff "have a grasp on a subject" is recorded from 1927.