Republican meeting unsettled army unit (8)
I believe the answer is:
regiment
'army unit' is the definition.
(I know that regiment is a type of army unit)
'republican meeting unsettled' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'unsettled' indicates anagramming the letters.
'meeting' anagrammed gives 'egiment'.
'r'+'egiment'='REGIMENT'
(Other definitions for regiment that I've seen before include "Organise; army unit" , "Section of an army" , "The Grenadier Guards, for example" , "Force under colonel" , "Order" .)