spine /ˈspaɪn/ noun
plural spines
plural spines
Learner's definition of SPINE
[count] : the row of connected bones down the middle of the back : backbone see picture at human
[count] : a sharp, pointed part on an animal or plant
[noncount] informal : courage or strength of character
[count] : the part of a book to which the pages are attached
◊ A book's spine often has the title and author's name printed on it.

up/down your spine

◊ If something sends a chill/shiver up/down your spine or if a chill/shiver runs up/down your spine, you become frightened, thrilled, etc.