Obtuse as this may be, fisherman finishes early (5)
I believe the answer is:
angle
'obtuse as this may' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'fisherman finishes early' is the wordplay.
'fisherman' becomes 'angler' (angler is a kind of fisherman).
'finishes early' means to remove the last letter (the word finishes before its final letter).
'angler' with its last letter taken away is 'ANGLE'.
'be' is the link.
Can you help me to learn more?
(Other definitions for angle that I've seen before include "possibly obtuse" , "member of tribe" , "Fish with hook and line" , "Ancient German, fish" , "The space where two lines intersect" .)