Tenacity shown by salesman overturned separation (12)
I believe the answer is:
perseverance
'tenacity' is the definition.
(thesaurus)
'by salesman overturned separation' is the wordplay.
'by salesman' becomes 'rep' (sales rep. I am not sure about the 'by' bit.).
'overturned' says the letters should be written in reverse.
'separation' becomes 'severance' (severance is a kind of separation).
'rep' backwards is 'per'.
'per'+'severance'='PERSEVERANCE'
'shown' is the link.
Can you help me to learn more?
(Other definitions for perseverance that I've seen before include "Determination" , "Tenacity, doggedness" , "Persistence, indefatigability" , "Continuing endeavour" , "Steady persistence" .)