Lopsi is the name of a (presumably) Illyrian tribe inhabiting the mountains along the eastern coast of the Adriatic before and during the Roman Empire, specifically present-day Velebit. The tribe was mentioned by Ptolemy in his Geographia, and after it was named one of the Roman cities on the coast, Lopsica (present day Sveti Juraj in Croatia).
The name has survived to present day as the name of several villages on the Velebit, in the form "Lopci", as well as the family surname Lopac.