1560s, "perfection," from exact (adj.) + -ness. Meaning "precision" is 1640s.
"precise, rigorous, accurate," 1530s, from Latin exactus "precise, accurate, exact," past participle of exigere "demand, require," literally "to drive or force out," also "demand, finish, measure," from ex- "out" (see ex-) + agere "drive, lead, act" (see act).
mid-15c., from Latin exactus, past participle of exigere (see exact (adj.)). Older in English than the adjective and retaining the literal sense of the Latin source. Related: Exacted; exacting.