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

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "syntax":
   IC analysis, allocation, allotment, apportionment, appositive,
   arrangement, array, arraying, attribute, attributive, collation,
   collocation, complement, constitution, construction modifier,
   cutting, deep structure, deployment, direct object, disposal,
   disposition, distribution, filler, form, form-function unit,
   formation, formulation, function, immediate constituent analysis,
   indirect object, levels, marshaling, modifier, object, order,
   ordering, phrase structure, placement, predicate, qualifier, ranks,
   regimentation, shallow structure, slot, slot and filler, strata,
   structure, structuring, subject, surface structure,
   syntactic analysis, syntactic structure, syntactics, tagmeme,
   underlying structure, word arrangement, word order



The Free On-line Dictionary of Computing (30 December 2018):

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)