Is this really a correct usage of word to say stomach instead of tummy especially when one's talking about her/is own body figure?

B/c personally I don't think it's correct,

the stomach should the organ inside a human body,

and the tummy is just the whole part of the body that covers up the area where the stomach locates.

Am I right?
stom·ach, n.

1. Anat., Zool.
a. a saclike enlargement of the alimentary canal, as in humans and certain animals, forming an organ for storing, diluting, and digesting food.
b. such an organ or an analogous portion of the alimentary canal when divided into two or more sections or parts.
c. any one of these sections.
2. Zool. any analogous digestive cavity or tract in invertebrates.
3. the part of the body containing the stomach; belly or abdomen.
4. appetite for food.
5. desire, inclination, or liking: I have no stomach for this trip.



'Tummy' is most commonly a word used by small children.

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i think it's right ...

sounds like it anyways !!
 Clive's reply was promoted to an answer.
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By small children do you actually mean youngsters?

I heard lot of Americans say tummy a lot, though.
Generally, "tummy" is what you say to children under 10 years old or so. It's a comical word when used between adults. You can use "tummy" with adults, but it will sound childish, but if the context is serious, always use "stomach".

Btw, the word "belly" or "gut" is often used for the stomach informally, although both generally refer to the entire abdomen (from the bottom of the ribs to the pelvis).