The Collaborative International Dictionary of English v.0.48:

Syntax \Syn"tax\, n. [L. syntaxis, Gr. ?, fr. ? to put together
   in order; sy`n with + ? to put in order; cf. F. syntaxe. See
   Syn-, and Tactics.]
   1. Connected system or order; union of things; a number of
      things jointed together; organism. [Obs.]
      [1913 Webster]

            They owe no other dependence to the first than what
            is common to the whole syntax of beings. --Glanvill.
      [1913 Webster]

   2. That part of grammar which treats of the construction of
      sentences; the due arrangement of words in sentences in
      their necessary relations, according to established usage
      in any language.
      [1913 Webster]

WordNet (r) 3.0 (2006):

syntax
    n 1: the grammatical arrangement of words in sentences [syn:
         syntax, sentence structure, phrase structure]
    2: a systematic orderly arrangement
    3: studies of the rules for forming admissible sentences

The Free On-line Dictionary of Computing (19 January 2023):

syntax

    The structure of valid strings in a given language,
   as described by a grammar.  For example, the syntax of a
   binary number could be expressed as

    binary_number = bit [ binary_number ]

    bit = "0" | "1"

   meaning that a binary number is a bit optionally followed by a
   binary number and a bit is a literal zero or one digit.

   The meaning of the language is given by its semantics.

   See also abstract syntax, concrete syntax.

   (1994-10-31)