Pronunciation: (kō-pûr'ni-kus, ku-),[key] —n. 1. Nic•o•la•us Pronunciation: (nik"u-lā'us),[key](Mikolaj Kopernik), 1473–1543, Polish astronomer who promulgated the now accepted theory that the earth and the other planets move around the sun ( the Coper'nican Sys"tem). 2. a crater in the second quadrant of the face of the moon, having an extensive ray system: about 56 mi. (90 km) in diameter from crest to crest with walls rising about 12,000 ft. (3650 m) from its floor; having several central mountains the highest being about 2400 ft. (730 m).