Etymology

(1) Formally this appears to straightforwardly represent the pres. ptcp. of the ME v. faren < OE faran ‘to go, travel, proceed, make one’s way’ (etc.) (cp. Go faran, OIcel fara, OFris fara, OS, OHG faran) and could be simply taken as such (so MED). Semantically, however, the use of the pres. ptcp. of the ON v. is a better fit than any of the senses otherwise attested in OE or ME, cp. OIcel fara in the sense ‘to suit, befit’ (see in particular CV  sense III.1 ‘to suit, fit, esp. of clothes, hair, or the like’), and (esp. when put next to the restricted medieval distribution of the English word) this leads several authorities to derive ME farand directly from an ON pres. ptcp. farandi (thus Bj. (claiming OWN origin in particular), Knigge 74, TGD, GDS (though also citing OE faran), McGee 327). (2) Alternatively, but perhaps less likely (see Bj. (DP 9 n.1 and Thomas 1913: 256), ME farand has been derived from a Celtic adj. represented by Gael. farranta ‘great, stout’, Ir forránta (farránta) 'bold, aggressive' (so e.g. Mätzner Wb. II. 76, Kullnick 27 (via Scots), Schmittbetz 12, Kaiser 1937: 198).  

PGmc Ancestor

(1) *faran-

Proposed ON Etymon (OIcel representative)

fara 'to move, go etc., to suit, befit'
(ONP fara (vb., praes. part.: farandi); farandi (sb.))

Other Scandinavian Reflexes

Far fara, Icel fara, Norw fara, Dan fare, Sw fara

OE Cognate

(1) faran 'to set forth, go, travel, wander, proceed'

Phonological and morphological markers

Summary category

D1c

Attestation

MED’s only indisputable instances of the adj. in this usage are given under its sense 15(b) ‘seemly, excellent, splendid’, and come otherwise from N alliterative texts and OED adds one in Sc.; mainly W., Sc. and Ir. in MnE dial (see McGee 514–15, Wright 1939: 18, EDD  sense (2)).  There are nonetheless a number of similar instances of what are more easily explicable as the pres. ptcp. of the v. faren under MED’s sense 15(a) (cp. OED sense 3), always preceded by an evaluative adv., from c1300 SLeg.(LdMisc 108) onwards, and without evident dial. restriction (cp. also EDD sense (1)).

Occurrences in the Gersum Corpus

Gaw 101; Pe 865; Cl 607, 1758; WA 2

Bibliography

MED faren (v.) (sense 15(b)) , OED farrand, farrant (adj.) , HTOED , EDD s.v. farrand (adj. and sb.), Dance farand, Bj. 209, 283, DP 8–9; (1) de Vries fara, Mag. fara, Bj-L. fare (1), Seebold far-a-, Orel *faranan, Kroonen *faran-, AEW faran, DOE faran, OED fare (v.1) ; (2) eDIL forránta , MacBain farral, farran