Swore fool’s practiced (7)
I believe the answer is:
assured
'swore' is the definition.
(assuring is a kind of swearing)
'fool's practiced' is the wordplay.
I cannot quite see how this works, but
'fool's' could be 'ass' (ass is a kind of fool) and 'ass' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for assured that I've seen before include "Gave confidence to" , "Sad ruse (anag.)" , "Confident, secure" , "without doubt" , "Self-confident" .)