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Results found in several dictionaries: Collins, Collaborative Dictionary
stomach ache , stomach-ache 
  n maux  mpl  d'estomac 
I have stomach ache.  J'ai mal au ventre. 

Collaborative Dictionary     English-French
body ache n. la douleur physique Reverso General Dictionary 
stomach flu n. la grippe intestinale Reverso General Dictionary 
sour stomachs n. les aigreurs d'estomac Reverso General Dictionary 
stomach ulcer n. un ulcère à l'estomac Reverso General Dictionary 
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'stomach ache' also found in translations in French-English dictionary
aigreurs d'estomac nmpl. sour stomachs Reverso General Dictionary 
mal aux reins pref. loins ache Reverso General Dictionary 

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