Something ring-shaped is a sign, we hear (5)
I believe the answer is:
torus
'something ring-shaped' is the definition.
(I've seen this in another clue)
'sign we hear' is the wordplay.
I cannot quite understand how this works, but
'we' could be 'us' and 'us' is present in the answer.
The remaining letters 'tor' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'is a' is the link.
Can you help me to learn more?
(Other definitions for torus that I've seen before include "Ring-shaped object" , "Doughnut-shaped figure" , "Doughnut-shaped solid" , "Architectural moulding" , "Ring shaped like doughnut with hole" .)