Polysemous expressions are words or phrases that have multiple related meanings. They differ from homonyms, where the multiple meanings are unrelated. Newspaper and wood are examples of polysemous expressions, as newspaper can refer to the company, physical paper, or edited work, and wood can refer to tree material or a forested area. In contrast, a homonym is a word that shares spelling and pronunciation with another word but has an unrelated meaning, like bow as a gesture of respect or a weapon.