1) to be disorderly
1a) of soldiers marching out of order or quitting ranks
1b) to be neglectful of duty, to be lawless
1c) to lead a disorderly life
Part of Speech: verb
Citing in TDNT: 8:47, 1156
From G813; to be (that is, act) irregular: - behave self disorderly.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root ἀτακτέω; click on the second column to search for that grammatical form of the root ἀτακτέω; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀτακτέω.