syntactical adj.

c. 1600, from French syntaxe (16c.) and directly from Late Latin syntaxis, from Greek syntaxis "a putting together or in order, arrangement, a grammatical construction," from stem of syntassein "put in order," from syn- "together" (see syn-) + tassein "arrange" (see tactics).

compound adjectival word-forming element, usually interchangeable with -ic but sometimes with specialized sense (such as historic/historical, politic/political), Middle English, from Late Latin -icalis, from Latin -icus + -alis (see -al (1)). Probably it was needed because the forms in -ic often took on a noun sense (for example physic). Forms in -ical tend to be attested earlier in English than their twins in -ic.