understated but complex in creation/concept or effect, in a way that is clever and delicate;
e.g. The painting is subtle but impactful.
having the ability to make fine distinctions and the insight to understand something deeply, having a refined sense of perception;
e.g. Her subtle analysis of the novel brought out the complexity of its themes.
using indirect methods or a gradual and understated approach in order to achieve something, typically employing cleverness and cunning;
e.g. The ministers hatched a subtle plan to gradually take away the king's authority.