The role of verbs in definitions is very complex. In general discourse, the functions of declarative sentences or propositions is to report events happening to participants, with verbs encoding the events and nouns the participants. In definitions of concepts, verbs and nouns are used to express, in the form of simple (stative) proposition, basic facts concerning processes, states, or actions that relate to the concepts mainly realised in noun form. While the nouns in the definienda can represent any class of concept, in this article it is argued that the verbs occurring in the second part of the definition, in finite form in the relative clause, can only represent activity or relation concepts because they serve to express states or conditions of existence, actions or executed processes.