1809, "first weekday after Christmas," on which by an English custom postmen, employees, and others can expect to receive a Christmas present; originally in reference to the custom of distributing the contents of the Christmas box, which had been placed in the church for charity collections. See box (n.1). The custom is older than the phrase.

Latin, hic iacet, "here lies," commonly the first words of Latin epitaphs; from demonstrative pronominal adjective of place hic "this, here" + iacet "it lies," third person singular present indicative of iacēre "to lie, rest," related to iacere "to throw" (from PIE root *ye- "to throw, impel").

1660s, cast iron, from iron (n.) + cast (adj.) "made by melting and being left to harden in a mold" (1530s), past-participle adjective from cast (v.) in its sense "to throw something (in a particular way)," c. 1300, especially "form metal into a shape by pouring it molten" (1510s). From 1690s as an adjective, "made of cast-iron;" figurative sense of "inflexible, unyielding" is from 1830.