Etymology

The OE reflex of the wk. 1 v. PGmc *fastjan-, formed on the adj. *fasta-, consistently appears as fæstan with /æ/, and therefore ought to have produced ME fast- in most dial (and the adj. stem does occur as fast- in the Gaw MS). It is therefore possible that the vocalism of ME fest- shows some input from ON, where the i-mutation of PGmc /a/ regularly gives /ɛ/ in this environment, cp. OIcel festa ‘to fasten; hang up; fix, settle, stipulate’ (and further OFris festa, OS festian, OHG festan)(thus McGee 328, Oakden I.78, Knigge 76, TGD, GDS). But an OE variant *festan is possible and the doublet ME fest- vs. fast- is closely paralleled by ME kest- vs. kast- (see kest (v.)) and could similarly be explained as a raising of ME /a/ > /e/ before /s/ plus another consonant, or present vs. past alternation.

PGmc Ancestor

*fastjan-

Proposed ON Etymon (OIcel representative)

festa ‘to fasten; hang up; fix, settle, stipulate’
(ONP festa (2) (vb.))

Other Scandinavian Reflexes

Far festa, Icel festa, Norw festa, Dan fæste, Sw fästa

OE Cognate

fæstan 'to fasten, make firm, ratify, establish'

Phonological and morphological markers

[i-mutation] (possibly diagnostic)

Summary category

CC2c

Attestation

ME fest- variants occur from c. 1300 onwards, and somewhat more regularly in N and E dial than elsewhere, though there are exceptions (e.g. c1300 Horn (LdMisc 108)).

Occurrences in the Gersum Corpus

Gaw 2347, WA 1259, 2230, 2320 etc.

For MS A festis at WA 3366 MS D has the better reading fraystes, and TPD (following the suggestion in Skeat's Glossary) accordingly emend to f[rai]stis 

Bibliography

MED fasten (v.1) , OED fast (v.1) , HTOED , Dance fest, Bj. 237, de Vries festa (2), Mag. festa, Heid. fasta-, Orel *fastjanan, AEW fæstan (1), DOE fæstan (1)