Etymology

Perhaps derived from ON, the further connections of this word are debated: (1) The ON v. represented by OIcel vappa ‘to waddle’ (taken as the source of the ME by Morris, followed by Kullnick 18) has WGmc cognates LG wappen, MDu wapperen ‘to swing’ (Orel and de Vries consider ME wappen as a cognate of, rather than a derivation on, the ON v.), but the etymological connections of PGmc *wap- cannot be securely traced as it likely 'of imitative origin' (Orel, de Vries). Attempts to find further related forms in Gmc and to suggest IE origins are, therefore, tentative and  somewhat contested (e.g. Mag., Torp-Falk 391, Pokorny 1114-5; see further Dance). (2) Some authorities have, therefore, simply taken the word as obscure (TGD, GDS and notably OED, comparing other ‘echoic’ forms (swap, whap, whop)). MED combines the two approaches, concluding ME wappen is likely of imitative origin, but also comparing ON vappa (but not the WGmc cognates).

PGmc Ancestor

(1) *wap-

Proposed ON Etymon (OIcel representative)

vappa ‘to waddle’ 
(ONP (1) vappa (vb.))

Other Scandinavian Reflexes

(1) Far vappa, Icel vappa, Dan dial vappe, Sw dial vapp

OE Cognate

Phonological and morphological markers

Summary category

DD1c

Attestation

Characteristic of N and alliterative texts, with the exception of MED’s sense (c) (‘To be plunged or driven (into an emotional state)’ (etc.).), which also occurs in Chaucer and Lydgate.

Occurrences in the Gersum Corpus

Gaw 1161, 2004; Cl 882; WA 2226

This reading is found only in the D MS of WA; the A MS variant of line 2226 reads: 'quirys out quarrels quappid thurʒe mayles'.

Bibliography

MED wappen (v.1) , OED wap (v.1) , HTOED , Dance wapped; (1) de Vries vappa, Mag. vappa, Orel *wappōjanan