-ac
(Greek > Latin: suffix; from French -aque, or directly from Latin -acus, from Greek -akos forming adjectives. This suffix was used to form names of arts and sciences in Greek and it is now generally used to form new names of sciences in English; meanings, "related to, of the nature of, pertaining to, referring to")
The suffix -ic has related elements.
Literally, a “circle of animal figures”; a narrow band in the sky in which the movements of the major planets, Sun, and Moon take place: The zodiac is astrologically divided into twelve sections named for the major constellations which are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.
