-ac, suffix
formerly -aque, -ak(e, -ack, primarily adj., whence also n. formative, repr. Gr. -ᾰκός, -ᾰκή, -ᾰκόν, the form of the adj. suffix -κός, in comb. w. n. in -ια, -ιος, -ιον, as καρδιακ-ός cardiac, of the heart, ἡλιακ-ός heliac, of the sun, δαιµονιακ-ός demoniac, belonging to a demon. Some of these were adopted in L. as cardiăc-us, dæmoniăc-us, elegīăc-us, aphrodīsiăc-us, on the model of which others as maniac-us, iliac-us have been formed in med. or mod.L. Thence they have been adopted in Fr. as learned words in -aque, partly from which, as in demoniac, partly from L. or Gr. they have been adopted in Eng. e.g. ammoniac, aphrodisiac, cardiac, celiac, elegiac, demoniac, hypochondriac, iliac, maniac, prosodiac, zodiac. See also -acal.