Various conjectures and comparisons have been offered, but most authorities consider the etymology of blunt in Pe 176 ('such a burre myʒt make myn herte blunt') uncertain. In the absence of an evident native etymon, comparisons have been made to the ON wk v. represented by OIcel blunda 'to have one's eyes shut, doze' (see also blunder). There are, however, formal and semantic objections to this explanation: Bj. and OED point out that the ON v. is intransitive and deriving a spelling in -nt from a pp. form blundað-r, blundat (there is no adj. blundr, only a masc. n. 'sleep, dozing') is unlikely. (Another hapax v. ME blunt 'to stagger, flounder' from Pat 272 ('til he blunt in a blok as brod as a halle') is perhaps more convincingly connected to blunda.) More speculative suggestions include a connection with blind (see further e.g. OED), but there is no compelling evidence to support ult. etymologies.
Proposed ON Etymon (OIcel representative)
blunda (v.) 'to have one's eyes shut, doze'
(ONP blunda (vb.))
Other Scandinavian Reflexes
Far blunda, Icel blunda, Norw blund(r)a, ODan blunde, Dan blunde, OSw blund(r)a
Phonological and morphological markers
Cited with this sense by MED and OED from Orrm onwards in a variety of texts (incl. Chaucer).
Occurrences in the Gersum Corpus
Anderson (AndPat 272n) argues it is better interpreted as an instance of blunt (v.).