Acetic means sour, acerbic. For example, lemons are acetic by taste. Or food kept for too long in the refrigerator goes acetic (sour).
Ascetic, on the other hand, refers to hermits and sages, one who have given up worldly pleasures and live a life of austerity. Ascetic means a life of rigorous self-discipline and self-denial; an abstainer: “Yogis in the Himalayas leas an ascetic life.”
Aesthetic or esthetic deals with an all together different subject: beauty. Aesthetic/esthetic means ‘characterized by a heightened sensitivity to beauty’. For example: “While buying a house, one should keep the aesthetic elements of design in mind’. (Aesthetic and esthetic mean the same).