Complete yet difficult progress (13)
I believe the answer is:
thoroughgoing
'complete' is the definition.
(I know that complete can be written as thoroughgoing)
'yet difficult progress' is the wordplay.
I cannot quite see how this works, but
'yet' could be 'tho' (tho' short for though) and 'tho' is found in the answer.
'difficult' could be 'rough' (similar in meaning) and 'rough' is present in the answer.
'progress' could be 'going' (I've seen this before) and 'going' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for thoroughgoing that I've seen before include "comprehensive" , "to the end" , "Extremely meticulous" , "Complete, absolute" .)