Can liar be used as an adjective to describe someone?

Answer 1

No, the word liar is a noun; a liar is the person.

The word to describe (adjective) a person who lies is lying; for example the lying phony or the lying witness.

To make it even more confusing, lying is also a verb (lie, lies, lying, lied).

Answer 2

It can be:

When a verb like "to lie" has an -ing at the end of it, it can be either a participle or a gerund.

A participle is when it still acts as a verb. An example of this would be "How do I know that you aren't lying?"

A gerund is when it acts as a noun. An example of this would be "Lying is one of his greatest skills."

So really, it depends on the context.

Answer 3

The noun 'liar' is a noun, a word for a person.