The Collaborative International Dictionary of English v.0.48:

Alphabetic \Al`pha*bet"ic\, Alphabetical \Al`pha*bet"ic*al\, a.
   [Cf. F. alphab['e]tique.]
   1. Pertaining to, furnished with, expressed by, or in the
      order of, the letters of the alphabet; as, alphabetic
      characters, writing, languages, arrangement. English has
      an alphabetical writing system.
      [1913 Webster]

   2. Literal. [Obs.] "Alphabetical servility." --Milton.
      [1913 Webster]

   3. in alphabetical order.

   Syn: abecedarian
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

alphabetical
    adj 1: relating to or expressed by a writing system that uses an
           alphabet; "alphabetical writing system" [syn:
           alphabetic, alphabetical] [ant: analphabetic]
    2: arranged in order according to the alphabet; "an alphabetic
       arrangement"; "dictionaries list words in alphabetical order"
       [syn: alphabetic, alphabetical] [ant: analphabetic]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "alphabetical":
   abecedarian, allographic, alphabetic, capital, graphemic,
   ideographic, lettered, lexigraphic, literal, logogrammatic,
   logographic, lower-case, majuscule, minuscular, minuscule,
   pictographic, transliterated, uncial, upper-case