<P> This leads to a corresponding distinction between nominal and real definitions . A nominal definition is the definition explaining what a word means, i.e. which says what the "nominal essence" is, and is definition in the classical sense as given above . A real definition, by contrast, is one expressing the real nature or quid rei of the thing . </P> <P> This preoccupation with essence dissipated in much of modern philosophy . Analytic philosophy in particular is critical of attempts to elucidate the essence of a thing . Russell described it as "a hopelessly muddle - headed notion". </P> <P> More recently Kripke's formalisation of possible world semantics in modal logic led to a new approach to essentialism . Insofar as the essential properties of a thing are necessary to it, they are those things it possesses in all possible worlds . Kripke refers to names used in this way as rigid designators . </P> <P> A homonym is, in the strict sense, one of a group of words that share the same spelling and pronunciation but have different meanings . Thus homonyms are simultaneously homographs (words that share the same spelling, regardless of their pronunciation) and homophones (words that share the same pronunciation, regardless of their spelling). The state of being a homonym is called homonymy . Examples of homonyms are the pair stalk (part of a plant) and stalk (follow / harass a person) and the pair left (past tense of leave) and left (opposite of right). A distinction is sometimes made between "true" homonyms, which are unrelated in origin, such as skate (glide on ice) and skate (the fish), and polysemous homonyms, or polysemes, which have a shared origin, such as mouth (of a river) and mouth (of an animal). </P>

What is a group of two things called