The word "runniest" is an adjective that describes something or someone that is flowing with a liquid or water, often in an uncontrolled or excessive manner. Some synonyms for the word "runniest" could include words such as "flowing", "gushing", "pouring", "spilling", "draining", "streaming", "rushing", "dripping", "weeping", "oozing" or "seeping". These words can be used to describe anything from a leaky faucet to a rushing river or even a person's tears. Each synonym lends a slightly different shade of meaning to the idea of something or someone that is "runniest", emphasizing different aspects of a particular scene or situation.