1832, "the theory or principle of a constitutional system of government;" occasionally also "constitutionality, adherence to constitutional government;" from constitutional (adj.) + -ism. Related: Constitutionalist (1766).
1680s, "pertaining to a person's (physical or mental) constitution," from constitution + -al (1). Meaning "beneficial to bodily constitution" is from 1750. Meaning "authorized or allowed by the political constitution" is from 1765. Constitutional monarchy is recorded from 1801, from French. Related: Constitutionally.
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/constitutionalism">Etymology of constitutionalism by etymonline</a>
Harper, D. (n.d.). Etymology of constitutionalism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/constitutionalism