Slide over and quickly get into (4,2)
I believe the answer is:
slip on
'get into' is the definition.
(slipping on is a kind of getting into)
'slide over and quickly' is the wordplay.
I cannot really understand how this works, but
'slide' could be 'slip' (slip is a kind of slide) and 'slip' is found in the answer.
'over' could be 'on' (physically on top of) and 'on' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for slip on that I've seen before include "easy to cope with when dressing" , "Type of garment" , "shoe, perhaps" .)