Limpet used to possess motivation (7)
I believe the answer is:
impetus
'motivation' is the definition.
(I've seen this before)
'limpet used to possess' is the wordplay.
'to possess' says the answer is hidden in the clue.
'IMPETUS' can be found hidden inside 'limpet used'.
(Other definitions for impetus that I've seen before include "Driving force, forward movement" , "Motivation" , "Momentum, stimulus" , "Driving force, momentum" , "Catalyst" .)