Accomplishment, indeed, yet is beaten (8)
I believe the answer is:
defeated
'is beaten' is the definition.
(similar in meaning)
'accomplishment indeed' is the wordplay.
I cannot quite see how this works, but
'accomplishment' could be 'feat' (feat is a kind of accomplishment) and 'feat' is located in the answer.
The remaining letters 'deed' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'yet' is the link.
Can you help me to learn more?
(Other definitions for defeated that I've seen before include "Whacked" , "foiled" , "Trounced" , "Beat; beaten" , "thwarted" .)