Semibreve
/ˈsemibriːv/
Definition 1 of 1
Pro Tip 1/3Music Notation
Understand that 'semibreve' refers to specific music notation and is used by musicians or in music theory. 
He marked the semibreve clearly on the score.
Pro Tip 2/3Time Signature
A semibreve's duration varies with time signature; it's not always four beats. 
In 3/4 time, you can't have a semibreve.
Pro Tip 3/3Instrumental Relevance
All musicians, regardless of instrument, use the semibreve to represent a long note duration. 
Even on drums, a semibreve indicates a sustained note.