The paper is concerned with determination of nature and cognitive realization of lexical polysemy. A primary goal is to identify the lexical prototype of the verbs «to tremble» and «to shake» that will help to draw the boundaries of their systemic meaning. Our procedure accounts for semantic differentiation of lexical items in the language system. The verb appears to have one systemic meaning, or its semantic core. All senses of the verb in speech evolve from the lexical prototype.