Adventist Youth Honors Answer Book/Music/Intervals
A half-tone - Semi-tone
A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music,and it is considered the most dissonant when sounded harmonically. It is defined as the interval between two adjacent notes in a 12-tone scale. For example, C is adjacent to C♯; the interval between them is a semitone.
Whole-tone scale, in music, a scalar arrangement of pitches, each separated from the next by a whole-tone step (or whole step), in contradistinction to the chromatic scale (consisting entirely of half steps, also called semitones) and the various diatonic scales, such as the major and minor scales (which are different arrangements of whole and half steps).
In classical music from Western culture, a third is a musical interval encompassing three staff positions, and the major third is a third spanning four semitones.
In music theory, a perfect fifth is the musical interval corresponding to a pair of pitches with a frequency ratio of 3:2, or very nearly so.
In music, an octave (Latin: octavus: eighth) or perfect octave is the interval between one musical pitch and another with half or double its frequency. It is defined by ANSI as the unit of frequency level when the base of the logarithm is two.