/ ˈtʌmi; NAmE / noun
( pl. -ies ) ( informal ) (used especially by children or when speaking to children) the stomach or the area around the stomach :
Mum, my tummy hurts.
to have (a) tummy ache
a tummy bug / upset (= an illness when you feel sick or vomit )
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WORD ORIGIN
mid 19th cent.: child's pronunciation of stomach .