A thesaurus is the correct answer. A thesaurus is a book that lists synonyms, or other words that mean the same thing. This will best help you find new ways to express your ideas. A dictionary simply defines a word, which could be somewhat helpful. A glossary is an alphabetized list found at the end of a book that includes new, uncommon, or specialized terms. Flashcards are a tool used to help study, so they would not be very helpful with learning new vocabulary.
Thesaurus will be most helpful because it will give you new words to use in your vocabulary it will express words in new ways which will in turn help your ideas be expressed differently
