constitutional (adj.)

mid-14c., constitucioun, "law, regulation, edict; body of rules, customs, or laws," from Old French constitucion (12c.) "constitution, establishment," and directly from Latin constitutionem (nominative constitutio) "act of settling, settled condition, anything arranged or settled upon, regulation, order, ordinance," noun of state from past-participle stem of constituere "to cause to stand, set up, fix, place, establish, set in order; form something new; resolve" (see constitute).

Meaning "action of establishing, creation" is from c. 1400; that of "way in which a thing is constituted" is from c. 1600; that of "physical health, strength and vigor of the body" is from 1550s; of the mind, "temperament, character" from 1580s.

Sense of "mode of organization of a state" is from c. 1600; that of "system of fundamental principles by which a community is governed" dates from 1730s; since the 1780s especially of the fundamental principles and rules of a government as embodied in a written document (as in the U.S. and France). In reference to Britain, the word was a collective name for the fundamental principles established by the political development of the English people embodied in long-accepted precedents. 

suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).