Mac adding strength of spirit to general excellence (10)
I believe the answer is:
waterproof
'mac' is the definition.
(I've seen this before)
'strength of spirit to general excellence' is the wordplay.
'strength of spirit' becomes 'proof' (I've seen this before).
'to' says to put letters next to each other (I've seen this in other clues).
'general excellence' becomes 'water' (I can't justify this - if you can you should give a lot more credence to this answer).
'proof' after 'water' is 'WATERPROOF'.
'adding' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for waterproof that I've seen before include "Mac" , "Impervious to rain" , "Rain-resistant" , "Impermeable" , "Protective garment" .)