Английский Этимологический словарь - swag (v.)

- 1530, probably from O.N. sveggja "to swing, sway," cognate with O.E. swingan "to swing" (see swing). The noun sense of "ornamental festoon" is first found 1794. Earlier senses of "bulky bag" (1303) and "big, blustering fellow" (1588) may represent separate borrowings from the Scand. source.