From Middle Valthungian blinkn, from Griutungi blinkan, cf. Gothic *bligkan, from ProtoGermanic blenkaną.
/ˈble̞n.ʧin/ v.wk.1ija trns. to blink, to flash, to flicker.
From Middle Valthungian blenkšjen, from Old Valthungian blenkjan, from Griutungi blankjan, cf. Gothic *blagkjan, from ProtoGermanic *blankijaną.
The main difference between these two terms is that the first is intransitive, while the second is transitive (or, more specifically, causative). E.g.:
blinkna: Þ·ōgana þis ǧužis blunkun.
‘The creature’s eyes blinked.’
blenčin: Þat ǧus blankiða is ǭgana.
‘The creature blinked its eyes.’