The purpose of this paper is to particularly examine the meaning of noun-to-verb conversion pairs by an intercategorical polysemic approach to denominal verbs. A noun-to-verb conversion in general occurs in English without any morphological change for linguistic economy. This conversion produces a denominal verb with its high productivity, in which its parent noun denoting an instrument is the most common, such as a noun to a verb conversion of ‘hammer’. However, all denominal verbs do not necessarily entail the meaning of parent nouns in the process of interpretation. That is, the semantic inclusion of a parent noun does not come into play to judge the semantic relatedness of a conversion pair, at which the meaning of hammerN is not explicitly indicated in hammerV. This semantic incompatibility between a parent noun and its derived verb is discussed in three respects: (1) the reason for diverse meanings, (2) the influential factors that determine the choice of meaning between them, and (3) the ways of understanding semantically unrelated pairs of conversion.