in the order of the letters of the alphabet: alphabetical arrangement.
pertaining to, expressed by, or using an alphabet: alphabetical writing.
Also, alphabetic.

1560–70; alphabet + -ical

alphabetically, adverb
nonalphabetic, adjective
nonalphabetical, adjective
nonalphabetically, adverb
prealphabetical, adjective
prealphabetically, adverb
unalphabetic, adjective
unalphabetical, adjective
unalphabetically, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
Cite This Source Link To alphabetical
World English Dictionary
alphabetical or alphabetic (ˌælfəˈbɛtɪkəl)
1.  in the conventional order of the letters or symbols of an alphabet
2.  of, characterized by, or expressed by an alphabet
alphabetic or alphabetic
alpha'betically or alphabetic

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Example sentences
Each chapter is introduced by a map and a geographical profile, followed by the
  parks in alphabetical order.
It lists them according to the intensity of the electronic relationship rather
  than in alphabetical order.
The letters line up on the right-hand side of the screen in alphabetical order,
  top to bottom.
The app lists the theorems in alphabetical order, or you can search for
  particular ones.
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