Topic summary
Augmented unison
Extracted from the Wikipedia article Semitone.
Augmented unison
The augmented unison, augmented prime, or chromatic semitone is the interval between two notes on the same staff position (same letter name) that differ by one chromatic alteration. For example, the interval between B♭ and B♮, or between C♮ and C♯, is an augmented unison.