This is the 8010th most frequent Turkish word.
köprünün
"Köprünün" means "of the bridge" or "the bridge's" in English.
Here, 'köprünün' is used in the genitive (possessive) case, indicating possession or relation with the noun it modifies 'üzerinden' (over/from above), forming the phrase 'from above of the bridge'.
Köprünün üzerinden bir araba geçti.
A car passed over the bridge.
In this sentence, 'köprünün' is in the genitive case, pairing with 'altındaki' to describe the location of the lake as 'under the bridge'.
Köprünün altındaki göl çok güzel.
The lake under the bridge is very beautiful.
'Köprünün' is again genitive here, relating to its repair (tamiri), indicating the item that is being repaired ('the repair of the bridge').