Sentence:  To find a place for them in their theory of knowledge would require them to revise the theory radically , and yet that theory was what they regarded as their <WSD>most</WSD> important discovery . 
Meaning of the word marked with <WSD> tags:  the superlative of `much' that can be used with mass nouns and is usually preceded by `the'; a quantifier meaning the greatest in amount or extent or degree