This is the 12369th most frequent Russian word.
капитану
"To the captain" (dative case).
In this sentence, "капитану" is in the dative case, indicating that the captain is the recipient of the action (receiving the map).
Мы передали капитану карту местности.
We handed the map of the area to the captain.
Here, "капитану" is in the dative case, expressing necessity or requirement for the captain.
Капитану корабля необходимо знать все маршруты.
The ship's captain needs to know all the routes.
In this example, "капитану" is again in the dative case, used to indicate the person being addressed or consulted.