This is the 7354th most frequent Polish word.
katolicki
"Katolicki" means "Catholic" in English.
In this sentence, 'katolicki' is an adjective qualifying the noun 'ksiądz' (priest), specifying his religious affiliation.
On jest katolicki ksiądz.
He is a Catholic priest.
Here, 'katolicka' is the feminine form of the adjective, describing the noun 'szkoła' (school) in accordance with its grammatical gender.
To jest katolicka szkoła.
This is a Catholic school.
The term 'katolickie' here is in the plural form, modifying 'tradycje' (traditions), conforming to grammatical agreement.