Written, composed, etc., on the spur of the moment; extemporized, hastily improvised.
Origin
Mid 17th century (in an earlier sense). From post-classical Latin autoschediasticus or its etymon ancient Greek αὐτοσχεδιαστικός extemporary from αὐτοσχεδιαστός extemporary (from αὐτοσχεδιάζειν + -τός, suffix forming verbal adjectives) + -ικός.