'brains'(Modern English harn)
Usually derived from ON, cp. OIcel hjarni 'brain' (< *herna before fracture and stress shift) because an OE (masc. or neut.) n. hærn(e) 'brain' is attested only once and very late, in a Peterborough Chronicle entry for 1137. PGmc *xerznan also appears in WGmc, cp. OHG hirni, MHG hirne, MLG herne. It is closely related to *xersnōn (cp. OIcel hjarsi 'crown of the head'), and further connected with e.g. Lat cerebrum 'brain'.
Proposed ON Etymon (OIcel representative)
(ONP hjarni (sb.))
Other Scandinavian Reflexes
Norw hjerne, Dan hjerne, Sw hjärna, hjärne
Phonological and morphological markers
This word first appears in English in ?a1160 Peterb.Chron. (LdMisc 636), and in ME is predominantly N and E. OED and EDD cite usage from N and Sc dial in MnE.
Occurrences in the Gersum Corpus
Pe 58; WA 839, 2545
The D MS of WA reads <harmes> at 2545.