What does the “-u” ending mean in Polish, like in “Kruku”?

In this fable, the fox flatters the raven by cooing “Kruku, kruku!” — not “kruk,” the word you’d find in a dictionary. Polish still uses a special form for direct address, the vocative: nouns like “kruk” (raven) become “kruku,” “Ania” becomes “Aniu,” and “mamo” is how you actually call your mom. Hear a name change shape, and you’ve spotted it.

Most masculine nouns ending in a hard consonant like -k, -g, or -ch take -u in the vocative — “ptak” (bird) → “ptaku,” “Bóg” (God) → the irregular “Boże.” It’s fading from casual speech among younger speakers, but it survives everywhere in fixed address: “Mamo!”, “Tato!”, “proszę pana” (roughly “sir”), and, of course, in fables where a clever fox needs to butter up a bird.