[a. Gr. ἐφιάλτης.
Usually believed to be agent-n. f. *ἐφιάλλεσθαι, var. of ἐφάλλεσθαι to leap upon, f. ἐπί on + ἄλλεσθαι to leap. But the phonological difficulties are considerable (cf., however, ἐφίορκος = ἐπίορκος, f. ἐπί + ὄφκος); and the synonymous ἠπιαλής, ἐφέλης, etc., suggest that the word may have been affected by popular etymology.]
A demon supposed to cause nightmare; nightmare itself.
1601. Holland, Pliny, II. 214. The diseases called Ephialtes or Incubus, i.e. the night-Mare.
1646. Sir T. Browne, Pseud. Ep., V. xxi. § 21. 272. To prevent the Ephialtes or night-Mare we hang up an hallow stone in our stables.
1656. Culpepper, Eng. Physic., 296. Such as in their sleep are troubled with the Disease called Ephialtes or Incubus.
1777. Brand, Pop. Antiq., 324. Ephialtes, or Night Mare is called by Common People Witch-riding.
