Akademik

Cretaceous
adj. & n.
—adj.
1 of the nature of chalk.
2 (Cretaceous) Geol. of or relating to the last period of the Mesozoic era, with evidence of the first flowering plants, the extinction of dinosaurs, and extensive deposits of chalk.
Usage:
Cf. Appendix II.
—n. Geol. this era or system.
Etymology: L cretaceus f. creta chalk

Useful english dictionary. 2012.