[1] epsilon 3782 (but without mention of Severus). See also iota 436 (without mention of Eutyches). Severus of Antioch↗ has an entry at sigma 271.
This heresy is described by Theodoretus in one of his Haeretic. fab., On Eutyches. See also Doctrina Patrum 58 (cf. 176.7). LSJ s.v. takes it as a sect 'without a known head': cf. Wace Dictionary of Christian Biography at web address 1. For the word in a different context, see alpha 853.