Sentence:  The <WSD>superlative</WSD> of "big" is "biggest". 
Meaning of the word marked with <WSD> tags:  The form of an adjective that expresses which of several items has the highest degree of the quality expressed by the adjective; in English, formed by appending "-est" to the end of the adjective (for some short adjectives only) or putting "most" before it.