balo

English "ball" is two words that happen to look alike. The dance came from French bal and Latin ballare. The round thing you kick is Germanic and unrelated - the two only became one English spelling by accident. Esperanto never merged them, so the three ideas keep three separate words and no context is ever needed:

• balo - a dance, an evening event.
• pilko - a ball you throw, kick or hit.
• balono - a balloon, or a ball filled with air.

French, which supplied the first of these, makes the same split for the same reason: un bal is a dance, une balle is a small ball, and balle is the Germanic word borrowed into French. The two French words are no more related than the two English ones. If you learn balo as a translation of English "ball" you will get it wrong roughly every time a child is involved.

Baleto is ballet, and it is literally a little balo - the Italian diminutive balletto did the same job before Esperanto existed. Around it: balsalono for a ballroom, maskobalo for a masked ball, and baladi is not a word - a ballad is balado, from the same root but arriving separately.