This is the 9903rd most frequent Polish word.
angielski
"Angielski" means "English" (relating to the English language or England).
Here, 'angielski' is declined as 'angielskiego,' describing 'języka' (language) in the genitive case.
Uczę się języka angielskiego, aby podróżować.
I am learning English to travel.
In this case, 'angielski' is the nominative form of the adjective turned into a noun, referring to the English language as a subject.
Angielski jest moim ulubionym przedmiotem w szkole.
English is my favorite subject in school.
Here, 'angielski' is used as an adjective describing 'słownik' (dictionary).