c. 1200, "made of adamant; having the qualities of adamant" (hard, unyielding, unbreakable, inflexible), from Latin adamantinus "hard as steel, inflexible," from Greek adamantinos "hard as adamant," from adamas (genitive adamantos) "unbreakable, inflexible," as a noun, "hardest material" (see adamant (n.)).
1620s, "to fasten with spikes," from spike (n.1). Meaning "to rise in a spike" is from 1958. Military sense (1680s) means "to disable guns by driving a large nail into the touch-hole." Figurative use of this sense is from 1823. Meaning "to lace (a drink) with liquor" is from 1889. Journalism sense of "to kill a story before publication" (1908) is from the metal spindle in which old-time editors filed hard copy of stories after they were set in type, or especially when rejected for publication. Related: Spiked; spiking.
also boot-leg, "upper part of the leg of a boot," 1630s, from boot (n.1) + leg (n.). As an adjective in reference to illegal liquor, 1889, American English slang, from the trick of concealing a flask of liquor down the leg of a high boot. Before that the bootleg was the place to secret knives and pistols. Extended to unauthorized music recordings, etc., by 1957.
1590s (transitive) "make hard;" 1620s (intransitive) "grow harder," from Latin induratus, past participle of indurare "to make hard, harden," from in- (from PIE root *en "in") + durare "to harden," from durus "hard," from PIE *dru-ro-, suffixed variant form of root *deru- "be firm, solid, steadfast." Related: Indurated.
coarse candy made from sugar or molasses boiled down and cooled, 1817, related to toffee, but of uncertain origin; perhaps associated with tafia (1763), a rum-like alcoholic liquor distilled from molasses, presumably of West Indian or Malay (Austronesian) origin (perhaps a Creole shortening of ratafia). On this theory, the candy would have been made from the syrup skimmed off the liquor during distillation.
"hardened skin," 1560s, from Latin callus, variant of callum "hard skin," related to callere "be hard," from Proto-Italic *kaln/so- "hard," but the PIE source is uncertain. Among proposed cognates are Old Irish calath, calad, Welsh caled "hard;" Old Church Slavonic kaliti "to cool, harden," Russian kalit "to heat, roast," Serbo-Croatian kaliti "to temper, case-harden."