From Wiktionary, the free dictionary
From ganga + af. Compare Gothic 𐌰𐍆𐌲𐌰𐌲𐌲𐌰𐌽 (afgaggan, “to go away, depart”).
ganga af
- to go off, go away, depart
- to go beyond
- to be left (as surplus)
- "ganga", Geir T. Zoëga (1910), A Concise Dictionary of Old Icelandic, Oxford at the Claredon Press, page 159