This is the 17748th most frequent Russian word.
украинец
"Украинец" means "Ukrainian (male)," referring to a man from Ukraine.
In this sentence, 'украинец' is used as a noun to denote the nationality/national identity of the person.
Он гордится тем, что украинец.
He is proud that he is Ukrainian.
Here, 'украинец' again functions as a noun describing a person's origin and indicating their cultural or national association.
Познакомьтесь, это наш новый сосед, настоящий украинец.
Meet our new neighbor, a true Ukrainian.
In this sentence, the word 'украинец' appears in its plural form 'украинцев,' referring to a group of people of Ukrainian nationality or ethnicity.