Homonyms are listed as separate entries in a dictionary, because lexicographers see them as unrelated in sense. A polyseme is a word which has several related senses. In many dictionaries you can find bank(1) and bank(2) as separate entries. The relation between the two is homonymy. Both of them are polysemes, because each of them has several definitions. Lexicographers make the distinction between homonyms and polysemes based on the intuition of native speakers as well as the etymology or history of words.