Stock obtained from one-time purchase (10)
I believe the answer is:
extraction
'stock' is the definition.
(thesaurus)
'one-time purchase' is the wordplay.
'one-time' becomes 'ex'.
'purchase' becomes 'traction' (as in grip on a surface).
'ex'+'traction'='EXTRACTION'
'obtained from' acts as a link.
(Other definitions for extraction that I've seen before include "Descent" , "drawing" , "breeding" , "Dental operation" , "one suffers with mouth open?" .)