This is the 201st most frequent Czech word.
ukrajina
"Ukrajina" in Czech means "Ukraine" in English.
Here, 'Ukrajina' is used as the proper noun referring to the country Ukraine.
Ukrajina je velká země na východě Evropy.
Ukraine is a large country in Eastern Europe.
In this case, 'Ukrajinu' is the accusative form of 'Ukrajina', indicating that the country is the target of the mentioned action.
Navštívil jsem Ukrajinu loni v létě.
I visited Ukraine last summer.
Here, 'Ukrajiny' is the genitive form of 'Ukrajina', showing possession, origin, or relationship.