Definitions

1. noun

In botany, a small cluster of stamens in flowers, especially in the family Ranunculaceae.

“The acis in the buttercup flower is a unique feature of its reproductive system.”

2. noun

In astronomy, a small, dark spot on the surface of the Sun, caused by a convective cell blocking the light.

“The solar astronomer studied the acis on the surface of the Sun to understand its behavior.”