the word “free” in the phrase “For free”, is it a noun, adjective, or adverb?
Adjective. “Free” describes the subject, which may or may not be specified in the phrase.
In the sentence “This is for free,” the subject is this, which is a noun (in this sentence it means a thing or idea) and the predicate is is for free. Our verb is is indicating existence and for free describes the subject “This.”