What word or phrase does your mother always say?
c.1400, "backbone," later "thornlike part" (early 15c.), from Old French espine (French épine), from Latin spina "backbone," originally "thorn, prickle," from PIE *spei- "sharp point" (cf. Latin spica "ear of corn," Old Norse spikr "nail;" see spike (n.1)). Meaning "the back of a book" is first attested 1922.
See spinal column.
Any of various short pointed projections, processes, or appendages of bone.