1540s, "not possessed in common," from un- (1) "not" + common (adj.). Meaning "not commonly occurring, unusual, rare" is recorded from 1610s. Related: Uncommonly.
he owed his greatest debt to his mother's uncommon character and ability
an uncommon liking for money
frost and floods are uncommon during these months
doing an uncommon amount of business
an uncommon sense of humor
she was kind to an uncommon degree