It’s about time. We are now on Instagram!
1620s, "one who appoints or elects a representative," from Latin constituentem (nominative constituens), present participle of constituere (see constitute). The notion is "to make up or compose" a body by appointing or electing a representative. As an adjective, "essential, characteristic," from 1660s; "that appoints or elects a representative to a body," from 1714.