Etymology

The only argument against ON derivation rests on an alternative reading of the MS (‘Lystily for laucyng þe lere of þe knot’): (1) MS <for laucyng> is read forlancyng by Madden (followed by Morris, TG etc. and OED) and explained as a prefixed form of ME lancen, launcen 'to throw' < AN, OFr lancer, lancier (< Lat lanceāre); cp. Fr forlancer 'to drive an animal from its lair'. (2) An ME v. forlancen would be unique, however, and most recent editors have followed GDS (1334n) in preferring to read <laucyng>, a vbl. n. on lausen, the v. formed on the adj. ME laus, lōs etc., derived from ON (cp. OIcel lauss 'loose, free (etc.)').

PGmc Ancestor

(2) *lausa-

Proposed ON Etymon (OIcel representative)

(2) lauss (adj.) ‘loose, free (etc.)’ 
(ONP (2) lauss (adj.))

Other Scandinavian Reflexes

(2) Far leysur, Icel laus, Norw laus, Dan løs, Sw lös

OE Cognate

(2)  lēas (adj.) without, free from

Phonological and morphological markers

[ON /au/ < PGmc */au/] (may not be applicable)

Summary category

D2

Attestation

(1) forlance is not recorded as a v. elsewhere by MED or OED. The uncompounded launcen is fairly widespread in ME from c1330(?c1300) Guy(1) (Auch) onwards.  (2) The vbl. n. lōsing(e) is recorded by MED from a variety of 14c. and 15c. texts (predominantly in medical contexts).  The v. ME lōsen is widespread from early ME; see further lausen.

Occurrences in the Gersum Corpus

Gaw 1334

Gaw MS <for laucyng> has been read as forlancyng (see Etymological discussion).

Bibliography

MED forlancen (v.) , MED lōsing(e (ger.2) , OED forlance (v.) , Dance laucyng; (1) AND lancer, DEAF lancier (v. tr.), FEW lanceare, MED launcen (v.) , OED lance (v.) ; (2) de Vries lauss, Mag. laus, Bj-L. løs, Heid. lausa-, Seebold -leus-a- (1), Orel *lausaz, Kroonen *lausa-, MED lōsen (v.3) , OED loose (v.) , OED loosing (n.) , Bj. 71