senatorial adj.

c. 1200, senatour, "member of a council of citizens invested with a share of the government of a state," specifically in reference to ancient Rome, from Old French senator (Modern French sénateur), from Latin senator "member of the senate," from senex "old; old man" (from PIE root *sen- "old").

Elder (n.) would be the native equivalent. Old English might also express the idea by folcwita. As "member of a (modern) governing body" from late 14c.; specifically in U.S. use from 1788. Fem. form senatress attested from 1731. The Senators was the name of the professional baseball team in Washington, D.C., from 1891 to 1971.

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)).