Registers in use in shops (5,2)
I believe the answer is:
tells on
This could be a double definition.
'registers in use' is the first definition.
The definition and answer can be both to do with communicating as well as being verbs in their -s form.
Perhaps there's a link between them I don't understand?
'shops' is the second definition.
(I've seen this before)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tells on that I've seen before include "Reports bad behaviour" , "shops" .)