Sentence:  If adjectival meanings show relatively low retentiveness of stems , as I am confident will prove to be the case in most languages of the world , why should our basic lists include 15 per cent of these unstable forms , but only 8 per cent of animals and plants which replace much more <WSD>slowly</WSD> ? 
Meaning of the word marked with <WSD> tags:  without speed (`slow' is sometimes used informally for `slowly')