1630s, "words used in a ceremony or ritual" (earlier as a Latin word in English), from Latin formula "form, draft, contract, regulation;" in law, "a rule, method;" literally "small form," diminutive of forma "form" (see form (n.)). Modern sense is colored by Carlyle's use (1837) of the word in a sense of "rule slavishly followed without understanding" [OED]. From 1706 as "a prescription, a recipe;" mathematical use is from 1796; chemistry sense is from 1842. In motor racing, "class or specification of a car" (usually by engine size), 1927.
