Etymology

This common n. has been explained (see esp. OED, McClure 'Personal names and the development of English') as a hypocoristic form of the name Gunnhildr. The first evidence for the name being applied to a weapon in ME comes from a 14c Latin document which refers to a giant cross-bow at Windsor as 'Domina Gunilda' ('Una magna balista de cornu quæ vocatur Domina Gunild'). Use as a common n. with a more generalized meaning 'siege engine that casts missile' is attested beginning in 1339. As well as the historical context, the first element of the name < PGmc *gunþz (cp. Burg *gunþs, OE gūþ (with Ingvaeonic loss of nasal consonant and compensatory lengthening)) provides a secure test of loan. 

PGmc Ancestor

*gunþz

Proposed ON Etymon (OIcel representative)

Gunnhildr (gunnr 'war' (poetic) + hildr 'battle')
(ONP )

Other Scandinavian Reflexes

OE Cognate

gūþ 'hostile encounter, battle, war'

Phonological and morphological markers

ON consonant cluster assimilation

Summary category

A1*

Attestation

The name 'Domina Gunilda' is attested in a Latin document of 1330-1 (see MED, OED) and the common noun becomes widespread shortly thereafter.

Occurrences in the Gersum Corpus

WA 2227

Bibliography

MED gǒnne (n.) , OED gun (n.) , HTOED , de Vries gunnr, guðr, Orel *ʒunþz, Kroonen *gunþī- ~ *gunþjō-