Sindarin for Dead Drop

I'm actually looking for a creative phrase that means dead drop, then a translation for that phrase. But dead drop sounds so modern!

In spy lingo, a dead drop is a place where one spy leaves a hidden message and another spy can (reasonably) safely pick it up. That way they don't easily endanger the other spy, they never actually have to meet at all.

Maybe a phrase like "place without meeting".

Or "Message Hollow", with linguistic roots based on "tree hollow".

Surprise us all with brilliant creativity! :)

Why not just "hidden place" Sad dholen or "secret place" Sad chûl.

There is a small, masked bird that makes a nest with a hidden entrance, the pendular tit. (I don't make up bird names!)

aew is small bird aedh is nest

Hidden nest would be aedh dholen? Or aedholen if compressed into simpler speech?

It seems an organic usage that might find its way into sindarin once the concept of a dead drop was invented.