One is charged nothing for entering home (3)
I believe the answer is:
ion
'one is charged' is the definition.
(I've seen this in other clues)
'nothing for entering home' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'for entering' means one lot of letters goes inside another.
'home' becomes 'in' (to be in is to be (at) home).
'o' going inside 'in' is 'ION'.
(Other definitions for ion that I've seen before include "Electrically charged particle" , "Particle (phys.)" , "Electrically charged atom or group of atoms" , "Electrically-charged particle" , "Charged atom/molecule" .)