Flak and Re-echo

Flak noun - Artillery designed to shoot upward at airplanes.

Re-echo and flak are semantically related In some cases you can use "Re-echo" instead a noun "Flak".

Re-echo noun - The echo of an echo.

Flak and re-echo are semantically related in consequence topic. Sometimes you can use "Flak" instead a noun phrase "Re-echo".