Anthelion. Faintly luminous disc seen in sky opposite Sun. Is due to reflection of Sun by ice particles in atmosphere.
Anticorrosive. Inimical to corrosion. Applied to paints, processes and preparations that are intended to prevent corrosion.
Anticyclone. Area of relatively high barometric pressure, around which wind circulation is clockwise in northern hemisphere, and anticlockwise in southern hemisphere. Generally associated with fine and settled weather. (Also called a High).