Terrific athletes originally with advanced skill (6)
I believe the answer is:
talent
'skill' is the definition.
(talent can mean a skill or ability)
'terrific athletes originally with advanced' is the wordplay.
'originally' indicates taking the first letters.
'with' means one lot of letters go next to another.
'advanced' becomes 'lent' (advance can mean to lend).
The first letters of 'terrific athletes' is 'ta'.
'ta'+'lent'='TALENT'
(Other definitions for talent that I've seen before include "Unit of currency" , "Sort of scout - old money - gift" , "Innate ability or Biblical money unit" , "money no longer usable" , "some scouts are looking for" .)