vinternat (OSw) vetrnætr (pl.) (ON) noun

The first day, literally night, of winter. In OSw, not specified as to the date, but in OIce and ONorw, 14 October, indicating certain legally significant time limits. In the plural, at least in OIce Grg, referring to the preceding Thursday and Friday night before the beginning of winter (on a Saturday).

beginning of winter ONorw GuL Llb, Olb
first day of winter OSw DL Bb
first night of winter OSw SdmL Bb
first winter’s night OSw HL Blb
Winter Nights OIce Grg Klþ 3 Lbþ 174
OIce Jó Llb 9, 21 Refs:

KLNM s.v.v. første vinterdag, sommerdag; Schlyter s.v. vinternat