Northern Ireland vehicle, silver, by centre of quay in Republic (9)
I believe the answer is:
nicaragua
'republic' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'northern ireland vehicle silver by centre of quay' is the wordplay.
'northern ireland' becomes 'NI' (abbreviation).
'vehicle' becomes 'car' (car is a kind of vehicle).
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'by' is a charade indicator (letters next to each other).
'centre of' says to take the centre.
The middle letters of 'quay' are 'ua'.
'ni'+'car'+'ag'+'ua'='NICARAGUA'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for nicaragua that I've seen before include "Central American republic" , "Central American state" , "Latin country" , "Central American nation" , "Central America country, capital Managua" .)