| Definition -
(1) The appropriate forming and arranging of words so that their relationship to each other in a sentence is shown.
(2) The area of grammar dealing with the established usages of grammatical construction and the rules deduced therefrom. As opposed to accidence, which deals with inflection. (OED)
(3) "The study of the principles and processes by which sentences are constructed in particular languages." (Noam Chomsky, Syntactic Structures, Introduction)
(4) "The system of rules that we use when putting words together." (Derek Bickerton)
Etymology - The word ultimately derives from the Greek syntaxis, a putting together (from syn, together + tassein, arrange).
Oxford English Dictionary - Its first citation in a language-specific sense is from 1613: "Syntaxe, construction and order of words."
(R. Cawdrey, Table Alphabeticall (ed. 3))