Malign type of business a republican supports (5)

I believe the answer is:

smear

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'malign' is the definition.
(I know this)

'type of business a republican supports' is the wordplay.
'type of business' becomes 'sme' (I can't explain this - if you can you should believe this answer much more).
'republican' becomes 'r' (abbreviation).
'supports' means one lot of letters go next to another (bottom letters provide a support for the top ones).
'sme'+'a'+'r'='SMEAR'

Can you help me to learn more?

(Other definitions for smear that I've seen before include "Dirty mark; aspersion" , "False report" , "Smother" , "Sully" , "Slanderous denigration of character" .)

I've seen this clue in The Irish Times.

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