1.
slow and fast; pace variation; modulation
the variation between slow and fast speeds or tempos; used in music, speech, and sports
To control the ball freely with varying speeds.
緩急自在 means having complete control over pace variation
2.
emergency; urgent situation
A crisis or emergency. Literary; it survives mainly in the set phrases 一旦緩急あれば and 一朝緩急あれば (should an emergency arise).
Composed of 緩 (slow, relaxed) + 急 (fast, urgent). The two senses come from different readings of this contrast: variation in speed (sense 1) versus the urgent end of the spectrum (sense 2).
Common expressions
- 緩急をつける: to vary the pace
- 緩急自在: having complete control over pace variation
- 緩急を使い分ける: to mix fast and slow skillfully
- 一旦緩急あれば: should an emergency arise (literary)
Usage
- Music: varying tempo for expressiveness
- Baseball: mixing fast and slow pitches
- Speech/writing: varying rhythm and pacing
- Sense 1 is the everyday one; sense 2 is literary and found almost only in 〜緩急あれば.