Noun
A note of half the time or duration of the breve; -- now usually called a whole note. It is the longest note in general use.
Source: Webster's dictionaryBy the same reckoning, there could be two or three of the next smallest note, the "minim," (equivalent to the modern "half note") to each semibreve. Source: Internet
The relation between the breve and the semibreve was called tempus, and the relation between the semibreve and the minim was called prolatio. Source: Internet