The confusion about "fruit" and "vegetable" arises because of the differences in usage between scientists and cooks.
Vegetables is more generally used of other edible parts of plants, includes:
Root crops: like potatoes, carrots and turnips.
Bulbs: like onions and garlic.
Stems: like asparagus.
Leaves: like lettuce and cabbage.
Flowers: like broccoli and cauliflower.
Scientifically speaking, a tomato is definitely a fruit.
In its strict botanical sense, the fleshy or dry ripened ovary of a plant, enclosing the seed or seeds.
Thus, apricots, bananas, and grapes, as well as bean pods, corn grains, tomatoes, cucumbers, and (in their shells) acorns and almonds, are all technically fruits.
This definition of fruit is very broad, and encompasses almost everything that contains seeds.
But... In 1887, the tomato reached the U.S. Supreme Court. The ruling? Vegetable. So legally, it seems, the tomato is not a fruit.
So, the answer to the question is that a tomato is technically the fruit of the tomato plant, but it's used as a vegetable in cooking.
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