OriginPossibly from Old Norse flaka (“to flutter, about”), which is ultimately imitative. Or, related to Old Norse flaga (“stone slab”), referring to the shape.
Formsflags(genitive, singular) · fløgg(plural) · flagg(indefinite, nominative, singular) · flaggið(definite, nominative, singular) · fløgg(indefinite, nominative, plural) · fløggini(definite, nominative, plural) · flagg(accusative, indefinite, singular) · flaggið(accusative, definite, singular) · fløgg(accusative, indefinite, plural) · fløggini(accusative, definite, plural) · flaggi(dative, indefinite, singular) · flagginum(dative, definite, singular) · fløggum(dative, indefinite, plural) · fløggunum(dative, definite, plural) · flags(genitive, indefinite, singular) · flagsins(definite, genitive, singular) · flagga(genitive, indefinite, plural) · flagganna(definite, genitive, plural)
Source: Wiktionary