Something I already knew: According to the scientific definition of flesh surrounding a seed or seeds, a tomato is a fruit.
Something I didn't know: In 1893, the US Supreme Court, for tariff purposes, legally declared the tomato to be a vegetable.
Something else I didn't know, but should have known: "Vegetable" is a purely culinary term, and has no scientific meaning whatsoever. The official difference between a fruit and a vegetable? Fruit is served with dessert, vegetables are served with dinner.