Welsh chieftain's scowl accepting death (9)
I believe the answer is:
glendower
'welsh chieftain's' is the definition.
'glendower' can be an answer for 'chieftain's' (I have seen 'revolting chieftain' mean 'glendower' so perhaps 'chieftain' could also mean 'glendower'). I'm not certain of the 'welsh' bit.
'scowl accepting death' is the wordplay.
'scowl' becomes 'glower' (I've seen this in another clue).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'death' becomes 'end' (synonyms).
'glower' placed around 'end' is 'GLENDOWER'.
Can you help me to learn more?
(Another definition for glendower that I've seen is " revolting chieftain".)