あめ means "rain" as noun. あめでした means "was rain.". "でした" is the past tense form of "です". "あめ" is a noun, so you can just connect with "です" or "でした" to make sentence. きのう means "yesterday". きのうは あめでした means "it…

きのう means "yesterday". あめ means "rain" as noun. あめでした means "was rain.". "でした" is the past tense form of "です". きのうは あめでした means "it was rain.".