Perëndi is an old Illyrian word for God and the sky, especially invoked in incantations and songs praying for rain. He was also an Illyrian god of thunder or storm-god. After the spreading of Christianity in Albania his name was and still is retained in Albanian as the ordinary designation for God.
Etymology
The word might be derived from perëndoj "to set (of the sun)", which might be borrowed from Latin parentare "to bring a sacrifice (to the dead), to satisfy" or Latin imperantem "ruling" (Alb. dielli perëndon "the sun sets", perhaps ultimately a calque on Greek ο ήλιος βασιλεύει "the sun sets", literally "the sun reigns").
Others see a connection to Indo-European *per(-kwu)- "oak god" or "thunder god" by possible association (see Perkwunos for a discussion of the possible etymologies of these groups of gods, the Perën- element might be related to Slavic Perun, from *per "to strike" perhaps, and the -di to *dyeus e.g. Greek Zeus). If this conjecture is correct, the word could have an "Illyro-Thracian" origin. In Albanian mythology, he is the consort of Prende.