nidan verb (upper class) with 'yu' ending (archaic), intransitive verb
Archaic intransitive Nidan verb. In modern Japanese, this meaning is expressed by 横になる or 寝る. The form 臥ゆ is found in classical literature and survives in a few compounds such as 臥所 (ふしど).
The archaic word 臥ゆ corresponds to modern Japanese 横になる (to lie down).