Old charitable company waived for taxing (7)
I believe the answer is:
onerous
'taxing' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for onerous that I've seen before include "Burdensome, heavy kind of duty" , "quite a burden if so" , "'Heavy, burdensome (7)'" , "Challenging" , "weight" .)