The crossword solutions for the term I, O or U are VOWEL (5 letters) and ELEM (4 letters). VOWEL is an English word that refers to a speech sound produced by the vocal cords. It is one of the two types of speech sounds, the other being consonant. ELEM is an abbreviation for element, which is a substance that cannot be broken down into simpler substances by chemical means. Elements are the building blocks of all matter in the universe.