Coin in slot? (6)
I believe the answer is:
invent
'coin' is the definition.
(I know this)
'in slot?' is the wordplay.
'slot?' becomes 'vent' (slot can mean a vent or opening).
'in'+'vent'='INVENT'
(Other definitions for invent that I've seen before include "Originate" , "Conceive" , "Devise (something new)" , "Make up (something false)" , "Be the first person to make something" .)