## Definition of prime

**:**the second of the canonical hours

**:**the first hour of the day usually considered either as 6 a.m. or the hour of sunrise

**:**the most active, thriving, or satisfying stage or period

- in the prime of his life

**:**the chief or best individual or part

**:**pick

- prime of the flock, and choicest of the stall
- —Alexander Pope

**:**prime number

**:**the first note or tone of a musical scale

**:**tonic

**:**the interval between two notes on the same staff degree

**:**the symbol ′ used to distinguish arbitrary characters (such as

*a*and

*a′*), to indicate a specific unit (such as feet or minutes of time or angular measure), or to indicate the derivative of a function (such as

*p′*or

*f′(x)*) — compare double prime

**:**prime rate