In this paper, we analyze metonymies involving the concept of "hand" in English and Spanish by making use of some of the analytical tools provided by cognitive linguistics. On the basis of the analysis, we argue that metonymies may be conventionalized on two levels: one related to the form of the conceptual mapping and another one related to the specific realizations of the mappings in a language. We also study how metonymic extensions may be based on metaphors. We further suggest that there is a correlation between the degree of genericity of a mapping and its likelihood of occurrence across languages. Finally, we show what cognitive principles underlie regularities in the cross-linguistic analysis and illustrate them with examples where there are full, partial, and no coincidences in the metonymic uses of the concept of "hand" in English and Spanish. (Olga I. Díez Velasco)