Tender secretary at length scrubbing back (7)
I believe the answer is:
painful
'tender' is the definition.
(similar in meaning)
'secretary at length scrubbing back' is the wordplay.
I cannot really understand how this works, but
'secretary' could be 'pa' (abbreviation for personal assistant) and 'pa' is located in the answer.
'at' could be 'in' (synonymous in some cases - eg at school, in school) and 'in' is located in the answer.
'length' could be 'l' (abbreviation in geometry) and 'l' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for painful that I've seen before include "Causing hurt, physical or mental" , "Agonising" , "Aching, hurtful" , "Distressing or hurtful" , "Tender" .)