What part of speech is subtle?

"Subtle" can be a few different parts of speech, depending on how it's used in a sentence:

* Adjective: This is the most common use. For example: "There was a subtle change in the painting's colors."

* Noun: This is less common, but can be used to mean "something subtle" or "a subtlety". For example: "The professor's subtle was lost on the students."

* Adverb: This use is rarer, and would be used in a way like "She subtly hinted at her plans."

The most common usage is as an adjective.