From Wiktionary, the free dictionary
From mega- + gift.
megagift (plural megagifts)
- (neologism) A donation to charity of millions of dollars.
2007 June 25, Stephanie Strom, “Absence of Major Disaster in ’06 Affected Giving”, in New York Times[1]:“These megagifts are beginning to show up in a way they haven’t before,” Mr. Jolly said.