Imprisonment wrongly used, keeping most of the others inside (7)

'imprisonment wrongly' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'keeping most of the others inside' is the wordplay.
'keeping' means one lot of letters goes inside another (some letters kept inside).
'most of' means to remove the last letter.
'the others' becomes 'rest' (eg the rest of a group).
'inside' becomes 'duse' (I can't explain this - if you can you should give a lot more credence to this answer).
'rest' with its last letter taken away is 'res'.
'res' put into 'duse' is 'DURESSE'.

'used' acts as a link.

Can you help me to learn more?