Yours, Etc.: Origins and Uses of 8 Sign-Offs
mid-15c., a legal term, "deviating from rule or principle, eccentric;" from Latin exorbitantem (nominative exorbitans), present participle of exorbitare "deviate, go out of the track," from ex- "out of" (see ex-) + orbita "wheel track" (see orb). Sense of "excessive, immoderate" is from 1620s; of prices, rates, etc., from 1660s. Related: Exorbitantly.