The Nagnatae (Ναγναται) or Magnatae (Μαγναται) were a people of ancient Ireland, recorded in Ptolemy's 2nd century Geography as living in northern Connacht. O'Rahilly suggests a connection between the Nagnatae and the Fir Ól nÉcmacht, a people of early Connacht, assuming a degree of corruption in the transmission of both names. For the town in their territory see Nagnata.
References
Nagnatae Wikipedia(Text) CC BY-SA