Meaning

noun a clam that is usually steamed in the shell

noun a cooking utensil that can be used to cook food by steaming it

noun a ship powered by one or more steam engines

originFrom steam + -er. The steamer duck or steamer (sense 6.2) is apparently named for its resemblance to a paddle steamer when swimming rapidly. The feces sense comically evokes the idea of steaming hot food and probably reflects that fresh feces sometimes give off visible water vapor in cold outdoor conditions such as those encountered by hunters, campers, and soldiers.

Etymology from Wiktionary, CC BY-SA 3.0