Trainee always takes time to make purchase (8)
I believe the answer is:
leverage
'purchase' is the definition.
(thesaurus)
'trainee always takes time' is the wordplay.
'trainee' becomes 'l'.
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'takes' says to put letters next to each other.
'time' becomes 'age' (age is a kind of time).
'l'+'ever'+'age'='LEVERAGE'
'to make' acts as a link.
(Other definitions for leverage that I've seen before include "What crowbar provides" , "Power to act effectively" , "financial advantage" , "Power of achievement; (US) gearing" , "Mechanical advantage; influence" .)