Trainee always has jemmy (5)
I believe the answer is:
lever
'jemmy' is the definition.
(I've seen this before)
'trainee always' is the wordplay.
'trainee' becomes 'l' (as in an L-plate for a learner driver).
'always' becomes 'ever' (synonyms).
'l'+'ever'='LEVER'
'has' is the link.
(Other definitions for lever that I've seen before include "Means of exerting force" , "Bar operating machinery" , "Crowbar" , "Bar turning on a fulcrum" , "Bar for prising something" .)