Kind of amphibian Manx bird fed marrow (2,1,6)
I believe the answer is:
to a degree
'kind of' is the definition.
(I've seen this in another clue)
'amphibian manx bird fed marrow' is the wordplay.
I cannot really understand how this works, but
'amphibian' could be 'toad' (toad is a kind of amphibian) and 'toad' is present in the answer.
'bird' could be 'ree' (I've seen this in other clues) and 'ree' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for to a degree that I've seen before include "Where university course may lead" , "Where undergraduate is heading" , "Up to a point" , "though not entirely" , "in some measure" .)