hrbat – back, spine (U), backbone
[Vukičević B, Rečnik štamparstva i izdavaštva en.sr/sr-en]


“TheFreeDictionary
…
backbone - the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved; "the title and author were printed on the spine of the book"”
( http://www.thefreedictionary.com/backbone )


“Merriam-Webster
…
Definition of SQUARE BACK
: a flat backbone of a book — compare round back “
( http://www.merriam-webster.com/dictionary/square back )

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Note added at 1 hr (2012-01-01 20:01:13 GMT)
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ili: flat spine


“Wiktionary
…
хрбат
Serbo-Croatian
1. spine, backbone
2. ridge, crest (hill, mountain, wave)
3. spine (narrow, bound edge of a book)”
( http://en.wiktionary.org/wiki/хрбат )


“Inward Bound
…
Flat spine: This construction contrasts with the rounded spine book . A stiff piece of board approximately the width of spine edge of the text block is joined to the book boards to create a case. In preparation for assembly, the signatures are carefully leveled (rather than curved) so that they rest flat against the spine of the book.”
( http://www.inward-bound.us/definitions.html )