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.
1872, from French centriste, from centre (see center (n.)). Originally in English with reference to French politics; general application to other political situations is by 1889.
Where M. St. Hilaire is seen to most advantage, however, is when quietly nursing one of that weak-kneed congregation who sit in the middle of the House, and call themselves "Centrists." A French Centrist is—exceptis eoccipiendis—a man who has never been able to make up his mind, nor is likely to. ["Men of the Third Republic," London, 1873]
<a href="https://www.etymonline.com/word/centrism">Etymology of centrism by etymonline</a>
Harper, D. (n.d.). Etymology of centrism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/centrism