Synonyms:
* Heavy: This is a more general term for a large amount of something, but it can be used to describe heavy rain.
* Drenching: This emphasizes the soaking effect of the rain.
* Pouring: This emphasizes the speed and intensity of the rain.
* Downpour: This is a more specific term for a heavy rain.
* Deluge: This is a more dramatic term for a heavy rain.
* Flood: This term is used when the rain is so heavy that it causes flooding.
Antonyms:
* Light: This is the opposite of heavy, and can be used to describe light rain.
* Drizzling: This describes a very light rain.
* Sparse: This refers to something that is thin or scattered, and can be used to describe rain that is not heavy.
* Dry: This is the complete opposite of rainy.
The best synonym or antonym to use will depend on the context of the sentence.