Why did Euclid name his book as "Elements"? What does "element" mean in this context? Does it relate to the nature of the book in some way? 
 A: In Greek it was called "Stoicheia"
"The question is, why were the elements, or the component primary parts of things, called stoicheia by the Greeks?  It is a word which has had a long history, and has passed from Greece to almost every part of the civilized world, and deserves, therefore, some attention at the hand of the etymological genealogist. 
Stoichos, from which stoicheion, means a row or file, like stix and stiches in Homer.  The suffix eios is the same as the Latin eius, and expresses what belongs to or has the quality of something.  Therefore, as stoichos means a row, stoicheion would be what belongs to or constitutes a row....
Hence stoichos presupposes a root stich, and this root would account in Greek for the following derivations:--
stix, gen. stichos, a row, a line of soldiers
stichos, a row, a line; distich, a couplet
steicho, estichon, to march in order, step by step; to mount
stoichos, a row, a file; stoichein, to march in a line
In German, the same root yields steigen, to step, to mount, and in Sanskrit we find stigh, to mount....
Stoicheia are the degrees or steps from one end to the other, the constituent parts of a whole, forming a complete series, whether as hours, or letters, or numbers, or parts of speech, or physical elements, provided always that such elements are held together by a systematic order."
