Bucket down is an idiomatic expression that means to rain heavily. However, there are several other synonyms to this expression, which can help us to express the same meaning in different ways. These synonyms include "pour down," "drizzle," "torrential rain," "heavy rain," "downpour," "cat and dog," etc. Each of these expressions can be used in different contexts, depending on the intensity of the rainfall, the time of the day, and the location. For instance, "torrential rain" can be used to describe a situation whereby the rain is heavy and persistent, "drizzle" can be used in describing light rain, while "heavy rain" can be used for a situation where the rain is intense and continuous.