The aim of the paper is to discuss vagueness of denominal adjectives in English in their qualitative usage. Semantic indeterminacy will be illustrated for selected denominal adjectives with the suffix –ial, focusing on the lexeme professorial. The range of the qualitative senses of such adjectives will be exemplified by sentences culled from COCA and other linguistic corpora. It will be argued that typicality effects (as discussed by Lakoff 1987) are relevant to the identification (and flexibility) of meanings of denominal adjectives.