*stéh₃mn̥ => στόμα and Pre-Greek => οὐρά
Stomach and stomatology are from the same root.
PIE *stéh₃mn̥, “mouth; muzzle”:
Avestan 𐬯𐬙𐬀𐬨𐬀𐬥, staman = “mouth [of a dog]”
Welsh safn = “mouth; jaws”
Hittite 𒅖𒋫𒈪𒈾𒀸, iš-ta-mi-na-aš /ištāman-/ = “ear”
Proto-Germanic *stebnō (despite Beekes's objections)
Russian у́стье ústje, "mouth of a river", у́стьице ústjice "little mouth of a river"
→ Ancient Greek: στόμα "mouth"
Of unknown Pre-Greek origin:
→ οὐρά "tail, rear"
+ suffix -χος (-khos):
1. στόμαχος - throat, gullet, stomach, bladder
2. οὐραχός - urachus, a foetal organ connected with the bladder