Etymology

Always derived from ON, cp. OIcel heill  'well-being' (originally neut., later fem.) formed on the adj. PGmc *xaila- (cp. Go hails 'healthy', OIcel heill 'whole, healed', OE hāl 'whole, uninjured, healthy', OFris hēl 'unhurt, whole, unharmed', OS hēl 'unhurt, unharmed', OHG heil 'whole, healthy, unscathed'); cp. similiarly OE hǣl, hǣlu (f.) '(state of) good health, cure, well-being' etc., OS hēli, OHG heila, heilī, OE hǣl (neut.) 'omen, good luck, safety', OS, OHG heil 'health, luck', Crimean Go iel 'good health'. See further Dance 2003: 359. 
In ME it is often used in place of the native n. (MED's hēle (n.(1)), as in the phrase wrothir haile, where the more usual form is wrōther hēle. 
MED suggests that the use of haille (n.) in the phrase ille haile could reflect direct input from the ON phrase represented by OIcel illu heilli 'unfortunate, unhappy' (see instances at ONP s.v. illr (adj.) sense (9)). The main evidence in support of this view is the clear N bias in the attestation of phrase.

PGmc Ancestor

*xail-

Proposed ON Etymon (OIcel representative)

heill (neut. and fem.) 'well-being'; cp. illu heilli 'unfortunate, unhappy'
(ONP heill (sb.) (f), heill (sb.) (n.); cp. illr (adj.))

Other Scandinavian Reflexes

Dan held, ODan held, OSw hel, häll

OE Cognate

cp. hǣl, hǣlu (f.) '(state of) good health, cure, well-being' etc., hǣl (neut.) 'omen, good luck, safety', hāl (adj.) 'whole, uninjured, healthy'

Phonological and morphological markers

ON /ei/ < PGmc */ai/

Summary category

A1*

(CC4c)

Attestation

First attested in ME from c1300(c1250) Floris (Cmb Gg.4.27) and thereafter more often in N texts, but with some widespread occurrences. The adj. is frequently attested earlier, from the 13c. A handful of instances of the phrase with this n. substituted for native hele begin to occur c. 1400 (see MED, OED).
The phrase ille haile is predominantly N, and notably used in Chaucer's Reeve's Tale. Also recorded as a surname from 13c. Worcestershire (MED). 

Occurrences in the Gersum Corpus

WA 1066, 1759

The A MS of WA reads <wrothirhaile> at 1759, while the D MS has <with euell haille>.  At WA 1066 the A MS reads <hilla haile> while D has a reading with a native phrase <euell hale>. Skeat WA reads it as an instance of haile (interj.), but see TPD 1190n. 

Bibliography