Slip trainee into team (5)
I believe the answer is:
slide
'slip' is the definition.
('slide' can be a synonym of 'slip')
'trainee into team' is the wordplay.
'trainee' becomes 'l'.
'into' means one lot of letters goes inside another.
'team' becomes 'side' (I've seen this before).
'l' inserted within 'side' is 'SLIDE'.
(Other definitions for slide that I've seen before include "Idles about on children's chute" , "Transparency" , "leading to a fall" , "Slip, slither, skid" , "Trombone part" .)