1802, from Modern Latin unilateralis, from unum, neuter of unus "one" (from PIE root *oi-no- "one, unique") + latus (genitive lateralis) "the side, flank of humans or animals, lateral surface," a word of uncertain origin. Jeremy Bentham (1748-1832) may have been the first to use it in the legal sense of "made or entered into by one party." Related: Unilaterally. Unilateral disarmament is recorded from 1929.
It is useless for the sheep to pass resolutions in favor of vegetarianism, while the wolf remains of a different opinion. [William Ralph Inge, "Outspoken Essays," 1919]
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/unilateralism">Etymology of unilateralism by etymonline</a>
Harper, D. (n.d.). Etymology of unilateralism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/unilateralism