What does "clutter up" mean?

To fill with rubbish or with needless articles.

What is a synonym for "clutter up"?

Common synonyms include: clutter.

verb

verb ·Rare ·Advanced level

Verb

1
To fill with rubbish or with needless articles. transitive
"Why do you clutter up your mind with such useless knowledge?"
2
fill a space in a disorderly way wordnet

"Why do you clutter up your mind with such useless knowledge?"