Diving bird endlessly showing signs of breathlessness (6)
I believe the answer is:
puffin
'diving bird' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for puffin that I've seen before include "diver" , "Bright-billed auk" , "Species of auk" , "Seabird with brightly coloured bill - sounds out of breath" , "Large-billed sea bird" .)