Sinus and Sinkhole

Sinus noun - An abnormal passage leading from a suppurating cavity to the body surface.

Sinkhole and sinus are semantically related. In some cases you can use "Sinkhole" instead a noun "Sinus".

Sinkhole noun - A depression in the ground communicating with a subterranean passage (especially in limestone) and formed by solution or by collapse of a cavern roof.

Sinus and sinkhole are semantically related. Sometimes you can use "Sinus" instead a noun "Sinkhole".