英语词源字典 - 在线词源网站

baker (n.)[baker 词源字典]: Old English bæcere "baker," agent noun from bacan "to bake" (see bake (v.)). In the Middle Ages, the craft had two divisions, braun-bakeres and whit-bakeres.
White bakers shall bake no hors brede..broune bakers shall bake whete brede as it comyth grounde fro the mylle withoute ony bultyng of the same. Also the seid broune bakers shall bake hors brede of clene benys and pesyn, And also brede that is called housholdersbrede. [Letterbook in the City of London Records Office, Guildhall, 1441]
Baker's dozen "thirteen" is from 1590s.
These dealers [hucksters] ... on purchasing their bread from the bakers, were privileged by law to receive thirteen batches for twelve, and this would seem to have been the extent of their profits. Hence the expression, still in use, "A baker's dozen." [H.T. Riley, "Liber Albus," 1859]
[baker etymology, baker origin, 英语词源]
thirteen (adj.): late 145c., metathesis of Middle English thrittene, from Old English þreotene (Mercian), þreotiene (West Saxon), from þreo "three" (see three) + -tene (see -teen). Similar formation in Old Saxon thriutein, Old Frisian thretten, Dutch dertien, German dreizehn, Old Norse threttan, Swedish tretton. As a noun from late Old English.

Not an unlucky number in medieval England, but associated rather with the customary "extra item" (as in baker's dozen). Superstitions began with association with the Last Supper, and the unluckiness of 13 sitting down together to dine (attested from 1690s). Most of the modern superstitions (buildings with floor "12-A," etc.) have developed since 1890.