Casimir \c(a)-si-mir\ as a boy's name is pronounced KAH-zee-meer. It is of Slavic origin, and the meaning of Casimir is "famous destroyer (of peace)". Associated with Poland for her famous 11th-century king, who brought peace to the nation. Also a saint's name (15th century).
For more information, see also the related name Casey.
A baby name that sounds like Casimir is Kazmer.