Etymology

The identification of ME forʒ in Gaw (‘A balʒ berʒ bi a bonke þe brymme bysyde, / Bi a forʒ of a flode þat ferked þare’) depends on what the spelling in <ʒ> is taken to stand for: (1) Earlier commentators and editors  (incl. TG, GDS, MED; see also Elliot 1984: 80) taking it to stand for /s/, favoured Sundén's explanation (1920: 141) that it should be identified with ME fors 'waterfall', probably derived from the ON n. represented by OIcel fors ‘waterfall; cascade of water, giant wave; rushing water course, turbulent stream’ < a PGmc *fursa-. (2) There are however no other instances of <ʒ> standing for final /s/ in a stressed monosyllable in the Gaw MS (we would expect <tʒ> in this position) and it is thus far more likely that <ʒ> here stands for late OE /x/, and the more plausible identification is then with ME forwe (PDE furrow) < OE furh ‘furrow, ditch, trench (made by a plough) (etc.)' (thus Emerson 1922: 405, Savage 1944: 349, followed by McGee 331, TGD, AW, Vant, PS etc.) representing PGmc *furxō (cp. OFris furch, MLG vore, OHG furh, furuh, OIcel for ‘drain, sewer’).  This makes good sense in context at Gaw 2173, if we assume the reference is to the channel of the stream.

PGmc Ancestor

(1) *fursa-; (2) *furxō

Proposed ON Etymon (OIcel representative)

(1) fors ‘waterfall; cascade of water, giant wave; rushing water course, turbulent stream’ 
(ONP (1)  fors (1) (sb.))

Other Scandinavian Reflexes

(1) Far forsur, Icel fors, foss, Norw fors, foss, Dan fors, fos, Sw fors

OE Cognate

(2) furh ‘furrow, ditch, trench (made by a plough) (etc.)'

Phonological and morphological markers

Summary category

DD2

Attestation

(1) MED’s only other citation for fors ‘waterfall’ is c1440 Degrev.(Thrn); but for N onomastic usage see EPNE and OED (and further EDD, Thorson 61–2).  (2) OE furh is widely attested (esp. in charter bounds), and its ME reflex is also widespread (albeit not cited by MED from before a1300(a1250) Bestiary (Arun 292)). 

Occurrences in the Gersum Corpus

Gaw 2173

Bibliography

MED fors (n.) , OED force (n.2) , OED furrow (n.) , HTOED , HTOED , EDD force (sb. 1), Dance forʒ; (1) de Vries fors (1), Mag. fors (1), Bj-L. foss, Orel *fursaz, Kroonen *fursa-, OED force (n.2) , EPNE fors; (2) MED fǒrwe (n.) , OED furrow (n.) , DOE furh, Bamm. 196, Orel *furxō, Kroonen *furh-