Queen endlessly sent up in Republic (5)
I believe the answer is:
niger
'republic' is the definition.
(I know that Niger is a republic)
'queen endlessly sent up' is the wordplay.
'queen' becomes 'regina' (Latin for 'queen').
'endlessly' means to remove the last letter.
'sent up' is a reversal indicator.
'regina' with its final letter removed is 'regin'.
'regin' reversed gives 'NIGER'.
'in' is the link.
(Other definitions for niger that I've seen before include "W. African country" , "West African republic" , "West African country, capital Niamey" , "West African river and country" , "Country W. of Chad" .)