Etymology

Formed within English on sere (adj.) + ME -lepy (shortened from onlepy 'single' (MED s.v. ō̆n-lẹ̄̆pī (adj.)); cp. serlepes (adv.). Sere (adj.) is probably an English development of sere (adv.), since no adjectival usage of ON sér is known (see OED). This adjectival form is only attested in WA. 

PGmc Ancestor

*sē-z

Proposed ON Etymon (OIcel representative)

sér 3 pers. sg. reflex. pron. (dat.)
(ONP sik (pron. pers. refl.))

Other Scandinavian Reflexes

OE Cognate

Phonological and morphological markers

Summary category

A2c

Attestation

This adjectival form is only known from WA; sere (adj.) occurs from Orrm onwards, mostly in the N and E.

Occurrences in the Gersum Corpus

WA 605, 4305, 4440 etc.

The A MS of WA reads <sereleps> at 4893 (describing werkes), which Skeat emends to *serelepis and TPD WA emend to *serelepe. TPD WA (4434n) explain the spelling <sullepe>  at WA 4305 following Hill's (1940) study of early loss of [r] before dentals, while Skeat simply notes 'put for surlepe' and MED also speculates it might be an error.

Bibliography

MED sẹ̄r(e-lẹ̄pī (adj.) , OED serelepy (adj.) , HTOED ; see further sere (adj.).