A capital gumboot (10)
I believe the answer is:
wellington
'a capital' is the definition.
(capital of New Zealand)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for wellington that I've seen before include "Kind of boot" , "way to serve beef tenderloin" , "City" , "Statesman" , "made to splash through the wet" .)