One mystery faced everyday by etymologists and philologists is why some words persist for centuries unchanged and why others last so little time. Today’s word, conch, has been in the Proto-Indo-European vocabulary for thousands of years. Conch comes to English from the Latin concha meaning a shellfish or mollusk and the Ancient Greek konkhe- meaning a mussel or shell, both from the PIE root *konkho-. The real mystery is why this word hasn’t changed in thousands of years, when people and cultures change so quickly and most countries have regional dialects so strong as to be on the verge of being indistinguishable. The family that conch belong to is the strombidae, from the Latin word strombus meaning spiral or twisted. Why did that word not survive into English but conch did? No one knows and probably no one ever will.
Black and white image of conch spirals by Joshua Davis. X-ray view of conch shell by Kevin Collins. Both used with permission under a Creative Commons 3.0 license.