Weak, though extremely willing (7)
I believe the answer is:
Here is my best explanation:
'weak' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'though extremely willing' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'willing' becomes 'ready' ('ready' is associated in meaning with 'willing').
'though' with its centre removed is 'th'.
(Other definitions for thready that I've seen before include "Like some yarn" and "Like some yarns".)