This is the 15289th most frequent German word.
unglücklichen
"Unglücklichen" means "unlucky" or "unfortunate" in English.
Here, 'unglücklichen' is used to describe the noun 'Katze' (cat) in the dative case, agreeing in gender and number.
Der unglücklichen Katze wurde geholfen.
The unfortunate cat was helped.
In this example, 'unglücklichen' is an attributive adjective describing the noun 'Mann' (man) in the accusative case, agreeing in gender and number.
Ich traf den unglücklichen Mann im Park.
I met the unhappy man in the park.
In this instance, the word 'unglücklichen' was supposed to reflect an attributive form; however, it should correctly be 'unglückliches' for agreement in case, gender, and number in standard German.