1A person who, or a thing which, rates something; (in early use especially) a person who fixes the rate for a tax, wage, etc.
A racing yacht with a rating (frequently specified by preceding numeral) which determines whether it is subject to a handicap when racing other yachts.
Early 17th century; earliest use found in Randle Cotgrave (fl. 1587–?1630), lexicographer. From rate + -er.