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Many swear words can be used as multiple parts of speech, such as s--t, which can be a verb, a noun, or an interjection. You might say that their use as interjections gives oaths a leg up on other words, so satisfying three parts of speech isn't too impressive. Merriam Webster lists four parts of speech for damn (noun, verb, adverb, and adjective). In the film "Blue Velvet," Dennis Hopper's character utters a sentence comprised almost entirely of the word "f--k" and its variations.
Getting out of the gutter, "book" can be an adjective (book learning), or a verb (we booked 2 tickets for the play, or when we heard the cops coming we knew it was time to book out of there ), in addition to a noun.
Merriam-Webster even lists a verb form of "word." (transitive senses : to express in words). Adding this arachaic verb form with the slang use of "word" as an interjection conveying agreement and/or approval, along with the common noun form, and you get three parts of speech.
