Sentence:  It is , however , a disarming disguise , or perhaps a shield , for not only has Mercer proved himself to be one of the <WSD>few</WSD> great lyricists over the years , but also one who can function remarkably under pressure . 
Meaning of the word marked with <WSD> tags:  a quantifier that can be used with count nouns and is often preceded by `a'; a small but indefinite number