What term refers to a cloud that is primarily associated with rain?

The term that refers to a cloud primarily associated with rain is "Nimbus." Nimbus clouds, particularly nimbostratus and cumulonimbus, are known for their ability to produce precipitation. Nimbostratus clouds are typically gray, thick, and cover the sky, resulting in continuous rain. Cumulonimbus clouds, on the other hand, are capable of producing heavy showers, thunderstorms, and even severe weather events like tornadoes.

In contrast, other cloud types serve different purposes; cumulus clouds are often fluffy and white with little to no precipitation, typically indicating fair weather. Stratus clouds are low-lying and can bring light rain or drizzle but are generally not associated with intense rainfall. Cirrus clouds, which are high and wispy, do not contribute to precipitation at ground level. Therefore, the association of Nimbus with rain clearly makes it the correct term in this context.