Synonyms:
* Folk song: This is a broad term that encompasses ballads, but also other traditional songs.
* Story song: This highlights the narrative aspect of a ballad.
* Lyric: This is a more general term for a song with words, but can sometimes refer specifically to a poetic verse.
* Song: This is the most general term, but it can be used to describe any musical piece with lyrics.
Antonyms:
* Opera: This is a much more complex and elaborate musical form.
* Symphony: This is a purely instrumental musical composition, without lyrics.
* Instrumental piece: This term covers a wide variety of music without lyrics, including symphonies, concertos, etc.
* Modern pop song: This is a very broad category that stands in contrast to the traditional, often narrative style of a ballad.
The best synonym or antonym will depend on the specific context in which you are using the word "ballad".