Sentence:  The first part of a compound word is either a <WSD>noun</WSD> (substantive, adjective, or numeral), an adverb, or a preposition, and in a very few cases a verb. 
Meaning of the word marked with <WSD> tags:  Either a word that can be used to refer to a person, animal, place, thing, phenomenon, substance, quality or idea, or a word that modifies or describes a previous word or its referent; a substantive or adjective, sometimes also including other parts of speech such as numeral or pronoun.