properly means men without a head.
A fraction among the Eutychians in the fifth century after the submission of Mongus their chief, by which they were “deprived of their head.”
Certain bishops exempt from the jurisdiction and discipline of their patriarch.
A sect of levellers in the reign of Henry I, who acknowledged no leader.
The fabulous Blemmyes of Africa, who are described as having no head, their eyes and mouth being placed elsewhere.
(Greek, a-kephale, without a head.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894