Become slower and Slow up

Slow up and become slower are semantically related in slow topic. In some cases you can use "Slow up" instead a verb phrase "Become slower", when it comes to topics like slow down.

Slow up verb - Lose velocity; move more slowly.

Become slower and slow up are semantically related in slow topic. You can use "Become slower" instead a verb "Slow up", if it concerns topics such as slow down.