Early 17th century; earliest use found in Edward Topsell (d. 1625), Church of England clergyman and author. From classical Latin aestīvus of or belonging to summer, occurring in summer, designed for, or used in, summer, appearing or growing in summer, in post-classical Latin also hot from aestus heat + -īvus. Compare Spanish estivo, Italian estivo, and also Old Occitan estiu, Catalan estiu, Spanish estivo, all nouns in sense ‘summer’.