Burrower out to sea? (4)
I believe the answer is:
mole
'burrower' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for mole that I've seen before include "Small spot - small mammal" , "Counterspy" , "spy a > breakwater" , "Subterranean mammal" , "one in the Underworld?" .)