A relative pronoun is a type of pronoun THAT is used to link two related ideas in a sentence. The most common relative pronouns are 'who, ' 'whom, ' 'whose, ' 'WHICH, ' and 'THAT.' The crossword solution for the term 'relative pronoun' is 'who, ' WHICH is a three-letter word. 'Who' is used to refer to people, and it can be used as a subject or an object in a sentence. For example, 'The person who wrote the book was very talented.'