Etymology

Always derived from ON, cp. OIcel angr ‘sorrow, resentment, distress; repentance; tribulation, injury’ with the -r as part of the stem indicating an original neut. es-stem (PGmc *angez- > *angaz-, cognate with Lat angor ‘strangling, anguish’). The same root is found in the OE adj. ange ‘anxious, painful, distressing’ (< PGmc *angu-; cp. OIcel ǫngr, Go aggwus, OHG ango) and the OE adj. enge ‘narrow; anguished; oppressive’ (< the variant *angwja- with i-mutation; cp. OFris enge, OS engi, OHG angi, engi, MDu enghe), but there is no sign of an es-stem outside of Scandinavian, and ON is therefore the most likely source of the ME. Most derive it directly from ON angr, though ODEE (followed by Bj-L) prefers to see it as a secondary formation on the ME v. angren (PDE anger) (itself < ON, cp. OIcel angra ‘to distress, grieve, trouble (etc.)’ (formed on angr)), which is attested slightly earlier in ME than the related n. It is also hard to rule out some input from Lat angor (MED). 

PGmc Ancestor

*angez- 

Proposed ON Etymon (OIcel representative)

angr ‘sorrow, resentment, distress; repentance; tribulation, injury’ 
(ONP angr (1) (sb.))

Other Scandinavian Reflexes

Far angur, Icel angur, Norw anger, Dan, anger, Sw ånger

OE Cognate

cp. ange (adj.) 'anxious, painful, distressing', enge (adj.) 'narrow, anguished, oppressive'

Phonological and morphological markers

Summary category

C1

Attestation

Fairly widespread in ME, though cited infrequently by MED before the later 14c. (earliest in a1325(c1250) Gen.& Ex.(Corp-C 444)).

Occurrences in the Gersum Corpus

Gaw 2344; Pe 343; Cl 572, 1602; Pat 411, 481; WA 750, 857, 1908 etc.

This word is faint and difficult to read at Gaw 2344 in the MS, but is regarded as legible by Knott 1915: 108 (see also Vantuono’s apparatus and McGillivray 2343–4n), and is so read by all editors.

Bibliography

MED anger (n.) , OED anger (n.) , HTOED , ODEE anger, Dance anger, Bj. 200, de Vries angr (2), Mag. angur (2), Bj-L anger, Heid. angu-, Orel *anʒaz, Kroonen *angaza-