"favoring imposed order over freedom," 1862, from authority + -an. Compare authoritative, which originally had this meaning to itself. The noun in the sense of "one advocating or practicing the principle of authority over individual freedom" is from 1859.
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.
<a href="https://www.etymonline.com/word/authoritarianism">Etymology of authoritarianism by etymonline</a>
Harper, D. (n.d.). Etymology of authoritarianism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/authoritarianism