The correct answer to what kind of word is the hyphenated word is 3. a compound adjective.
The hyphenated word is a compound adjective. <em>It comes after the verb to be, which is a linking verb, modifying or specifying the noun "dreams".</em> The dreams in the sentence would be stiff and frozen at the same time (also, stiff because they are frozen), so, "stiff-frozen". That expresses <em>the dreams' characteristic, therefore, it consists of a compound adjective.</em>
The correct answer couldn't be <em>1. a compound verb</em>, because<em> "stiff-frozen" doesn't consist in an action, thus, it can't be considered a verb.</em> It expresses a characteristic, that's why it is an adjective.
The correct answer couldn't be <em>2. a compound noun</em>, because <em>it doesn't consist of people, place or thing.</em> It is a characteristic, hence, a compound adjective.
The correct answer couldn't be <em>4. a compound adverb</em>, because<em> "stiff-frozen" isn't modifying a verb, but a noun</em>, and therefore it can be understood as an adjective and not an adverb.
