This is the 8369th most frequent Russian word.
моравецкому
"Моравецкому" is the dative or prepositional case of "моравецкий," which relates to "Moravian" (pertaining to Moravia, a region in the Czech Republic).
Here, 'моравецкому' is used as a dative-form adjective derived from 'Моравецкий', relating to Moravia, attributing the quality to a friend.
Я написал письмо моравецкому другу из Чехии.
I wrote a letter to my Moravian friend from the Czech Republic.
In this example, 'моравецкому' modifies 'послу' (ambassador) in the dative case, specifying the nationality or origin.
Мы отправили приглашение моравецкому послу на конференцию.
We sent an invitation to the Moravian ambassador to the conference.
Here, 'моравецкому' describes 'клубу' (club) in the dative case, identifying it as related to Moravia.