Mid 17th century; earliest use found in Thomas Fuller (1607/8–1661), Church of England clergyman. From post-classical Latin admissivus admissible, already in classical Latin (as admissīvus) in sense ‘that gives a favourable omen’, of birds used in soothsaying (recorded in an 8th-cent. epitome of a 2nd-cent. grammarian) from classical Latin admiss-, past participial stem of admittere + -īvus.