This is the 7284th most frequent Japanese word.
丸く
"丸く" means "roundly" or "in a round shape."
Practically describing the shape of an object, in this case, '丸く' indicates the roundness of the stone.
その石は丸くなっている。
That stone is rounded.
Metaphorically describing an abstract concept, in this instance, '丸く' suggests the softening or becoming more pleasant of her personality.
彼女の性格は丸くなったと思う。
I think her personality has softened.
Functionally describing an action to create rounded edges on a surface, with '丸く' focusing on the desired shape of the corners.