I know, that most of you will think, that it is absurd, but please read to the end.
Sorry for my English
When I read the Ostrog Bible I saw, that in the OCS the verb "to unbend a book" was used (instead of "to open a book").
At the first onset I thought about a knee, because in Russian we use that verb with this noun.
Whereupon I thought, that the English/German word knee/Knie is consonant to the first part of the OCS word "kniga".
Thereupon I thought, that the Old Slavonic laguage has a borrowed words, where "ga" is a suffix (for an example, French cheval "a horse" -> Old Slavonic chevlaga/chevluga "an old horse").
Thereupon I thought, that if someone doesn't have a table he put his "kniga" on a "knee".
Thereupon I thought, that the English verb "unbend" translates to German "geradebiegen".
Thereupon I thought about Bogen (bow), Bucht (bight) and Buch (book).
Thereupon I thought, that a knee bore little comparison to a book spine.
Thereupon I got an answer, that "The English use of 'spine' for that part of a book is modern, only from the early 20th century. Before that, this part of the book was generally known as the 'back' "
Question: Does the English word "back" somehow relate to "book"? I can not imagine a book without a back.
The official etymology: