the word 'succubus' entered english in the late 14th century from medieval latin, where it denoted a female demon. the latin term itself is an alteration of the late latin 'succuba' ("prostitute"), which derives from the classical latin verb 'succubare', meaning "to lie under." this verb is a compound of 'sub-' ("under") and 'cubare' ("to lie down"). the literal sense of "lying under" evolved into the specific mythological concept of a demon that lies upon sleepers. this contrasts with the male counterpart, an 'incubus', from latin 'incubare' ("to lie upon"). the modern figurative sense of a draining or predatory entity logically extends from the demon's legendary energy-sapping nature.

the word is a direct loan from latin and functions as a simplex unit in english. its latin components are not directly separable in the modern english spelling without altering their form (e.g., 'sub-' + 'cubare').