The phrase "lash down" means to beat down or pour heavily, usually in reference to rain or hail. There are several synonyms for this phrase, including "pelt," "pound," "hammer," "beat," and "blast." Each of these words emphasizes the force and intensity of the precipitation, making it sound even more severe. Other synonyms include "drum," "thunder," "bucket," "drench," and "deluge," all of which imply a torrential downpour. These words can be used to describe a storm that is particularly noteworthy or damaging, or to paint a vivid picture of the weather in a piece of literature or storytelling.