Government department tax on small motors (8)

I believe the answer is:
ministry
'government department' is the definition.
(ministry is a kind of government department)
'tax on small motors' is the wordplay.
'tax' becomes 'try' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'small motors' becomes 'minis' (I can't justify this - if you can you should believe this answer much more).
'try' put after 'minis' is 'MINISTRY'.
Can you help me to learn more?
(Other definitions for ministry that I've seen before include "service" , "a cleric has entered" , "cloth?" , "Priests' work" , "members of the clergy" .)
