: a musical notation originating in the 13th century consisting of single notes (as large, breve) and ligatures each with a definitely fixed time value and thereby making possible the combination of independent voice parts that led historically to the development of counterpoint and the modern notation
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a system of musical notation of the 13th to the late 16th centuries, marked by the use of note symbols such as the longa and brevis, the absence of bar lines and ties, and the equivalence in value of one note to either two or three of the next smaller degree.
Useful english dictionary. 2012.