For music:
* Slow: If "tempo" refers to the speed of music, "slow" is a direct opposite.
* Lento: A specific musical term for a very slow tempo.
* Adagio: A musical term for a slow tempo, though slightly faster than "lento."
For general speed:
* Slowness: If "tempo" refers to the pace of something, "slowness" is the antonym.
* Delay: This implies a purposeful slowing down or interruption.
* Stasis: This suggests a complete lack of movement or change.
For rhythm:
* Atonality: While not exactly an antonym, this refers to music that lacks a clear sense of rhythm or meter.
* Dissonance: This refers to music that sounds jarring or unpleasant, often due to a lack of rhythmic coherence.
It's important to consider the specific context in which "tempo" is used to find the most accurate antonym.