noun

• (grammar, uncountable) Change in the form of a word (morphologic change) to express different grammatical categories.
• (grammar, countable) An instance of such change.
• (grammar) An affix representing such an instance.
• (grammar, countable) Any form produced by such an instance of a change, such as the principal parts for any given stem: any of the declined or conjugated forms that constitute its declension or conjugation.
• A change in pitch or tone of voice.
• (mathematics) A change in curvature from concave to convex or from convex to concave.
• A turning away from a straight course.
• (optometry) Diffraction.