callus n.

c. 1400, "hardened," in the physical sense, from Latin callosus "thick-skinned," from callus, callum "hard skin" (see callus). The figurative sense of "unfeeling, hardened in the mind" was in English by 1670s. Related: Callously; callousness.

King Arthur's sword, c. 1300, from Old French Escalibor, corruption of Caliburn, in Geoffrey of Monmouth (c.1140) Caliburnus, apparently from Welsh Caledvwlch probably a variant of the legendary Irish sword name Caladbolg which might mean literally "hard-belly," i.e. "voracious." For first element, see callus; for second, see belly (n.).

dance tune of Spanish origin, 1650s, from Italian, from Spanish pasacalle, from pasar "to pass" (from Latin passus "step, pace," from PIE root *pete- "to spread") + calle "street," from Latin callis "path, rough track" (which is perhaps related to callum "hard skin;" see callus). So called because the songs often were played in the streets.