Weakened through heat? (9)
I believe the answer is:
qualified
'weakened' is the definition.
(qualify can mean to weaken or make conditional)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for qualified that I've seen before include "Professional" , "Passed exams - with reservations" , "Having credentials" , "Provided with the attributes necessary to do a job" , "guarded" .)