egg

An egg is the shell-covered, roundish object that's laid by birds and reptiles, which usually has an embryo inside. When an egg hatches, a baby chick, snake, or lizard comes out.

Fertile eggs are the ones that become animals, while those laid by infertile birds are the kind you eat, scrambled or fried, for breakfast. The ovum, a reproductive cell in female animals, including humans, is also an egg. Colloquially, if you "lay an egg," you make a total mess of something, and if you "have egg on your face," you look foolish. If, however, you're considered a "good egg," you're a pal or a nice person.