Beatrice says Benedick is “a valiant trencherman” and has ”an excellent stomach.” This is a play on words. What is she actually saying?

Beatrice is playing with words. Beatrice is making fun of t Benedick when she calls him a "valiant trencherman" or a "hearty eater" to have a stomach  or courage. Basically Beatrice calls Benedick a courageous eater instead of a courageous man.