The only attested form, reste, can be interpreted as either resté (with the tonic e of a past participle form) or as the feminine form of rest. English borrowings as both rest and resty confirm the validity of both interpretations. The boz Char citation has the word rhyming with beste, and corroborates the atonic form. In all other attestations, the word may also be read as resté. The OED suggests an etymology from the past participle of rester (‘left over, remaining’).