tvímánuðr (ON) tvímánaðr (ON) noun

‘Double-month’. The fifth month of summer, which normally began on Tuesday, 12–18 August. It may have been used as a synonym for the summer month called heyannir.

double month OIce Grg Þsþ 80
ONorw GuL Llb
ONorw MLL Llb 40 Refs:

CV s.v. tvímánuðr; Fritzner s.v. tvímánaðr; GAO s.v. Misseristal; GrgTr I:129; Hertzberg s.v. tvímánaðr; KLNM s.v. månadsnamn