Douglas Harper's Etymology Dictionary
unsystematic
1770, from un- (1) "not" + systematic (adj.).
Wiktionary
unsystematic
a. Not systematic
WordNet
unsystematic
adj. lacking systematic arrangement or method or organization; "unsystematic and fragmentary records"; "he works in an unsystematic manner" [ant: systematic]
Usage examples of "unsystematic".
The Dwarves of Moria, as can be seen, introduced a number of unsystematic changes in value, as well as certain new _cirth:_ 37, 40, 41, 53, 55, 56.
Even when her own loyalty to New Crobuzon was such an odd, unsystematic thing, she could not help thinking of Johannes as a kind of turncoat.