Etymology

Late OE cost, ME cost is usually now derived from ON, cp. OIcel kostr ‘condition, choice, opportunity (etc.)’. The ON n. is normally declined as a masc. i-stem (of the staðr type, without i-mutation), but occasionally has acc. pl. -o, -u as if a u-stem.  It may therefore represent the continuation of two originally distinct nominal derivations on PGmc *kust-, both of which are attested elsewhere in Germanic: on the one hand PGmc *kust-iz (fem.), cp. OE cyst ‘choice; excellent, precious thing; merit (etc.)’, Go gakusts ‘test’, OFris kest ‘choice’, OS kust, OHG chust, kust; and on the other PGmc *kust-uz (masc.), clearest in Go kustus ‘test’.  Early OE only attests the fem. and mutated i-stem cyst and thus commentators derive late OE cost (masc.) < ON kostr (masc.).  Some have, nonetheless, explained OE cost as a native representative of the Gmc u-stem (e.g. AEW, GED, Bammesberger 157, Seebold), reworked as an a-stem (perhaps relatively early in WGmc; cp. OHG kost). SPS (108–9) further draws attention to the widespread OE costian ‘to prove, test, try; tempt’ and is sceptical of the need to invoke ON input.

PGmc Ancestor

*kust-iz or *kust-uz

Proposed ON Etymon (OIcel representative)

kostr ‘condition, choice, opportunity (etc.)’
(ONP kostr (1) (sb.))

Other Scandinavian Reflexes

Far kostur, Icel kostur, Norw kost, ODan kost, Dan kost, OSw koster

OE Cognate

cyst 'free-will, choice'; cp. costian ‘to prove, test, try; tempt’

Phonological and morphological markers

Summary category

C1ac

Attestation

Several occurrences in later OE texts (see Peters 89, Pons-Sanz 2007: esp. 163–164, 208–209, 240 and SPS 108–9, 286).  Widespread in early ME, but by the later period mainly N and E and alliterative (inc. PP), with a few exceptions (esp. in the phrase nedes cost).

Occurrences in the Gersum Corpus

Gaw 546, 750, 944, etc.; Cl 1024, 1478

Gaw 750 costes is interpreted by OED (only) as a derivative of OFr cost (s.v. cost n.2, sense 3, ‘expenditure of time, labour’); on the sense here see further Emerson 1922: 374, Wright 1935: 169.

Bibliography

MED cost (n.1) , OED cost (n.1) (cost (n.2) , HTOED , HTOED , HTOED , Dance cost, Bj. 247, SPS 108–9, 286, de Vries kostr (1), Mag. kostur (1), Seebold keus-a-, Bammesberger 140, 157, Orel *kustiz; *kustuz, Kroonen *kusti-; *kustu-, AEW cost (1), DOE cost n.2