Kap·ton·bul
late 21c., most likely from greek káto apó tin póli „under the city“ analogous to the derivation of Istanbul from eis tin pólin „into the city“, sometimes derived from latin capere „to grasp, take, conquer“ / captus „prisoner“, or turkish kap „vessel“ / kaptan „captain“
Meaning: Colloquial Name for the network of man-made caverns below Istanbul