spine Look up spine at Dictionary.com
c.1400, "backbone," later "thornlike part" (1430), from O.Fr. espine (Fr. épine), from L. spina "backbone," originally "thorn, prickle," from PIE *spei- "sharp point" (cf. L. spica "ear of corn," O.N. spikr "nail;" see spike (n.1)). Meaning "the back of a book" is first attested 1922. Spineless in fig. sense of "irresolute" is from 1885. Spine-chiller "mystery film" is attested from 1940; spine tingler in same sense is from 1942.