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How to understand and remember the Polish nominative plural form? [9]
1. Look at the noun in its singular form.
2. Try to pronounce it in a way that's easier to do so.
3. Check the correct version.
Eventually you should get a grasp. It's a bit of a dick advice, but I don't think there's much point in learning the endings of every word. The plural form isn't as irregular as it is in German, anyway.
Anyway
ta macierz - te macierze
ta klacz - te klacze
So I think the endings are -e in both cases. Hard to explain why though.
macierz - matrix; klacz - mare
edit: just re-read your post and realized you gave the example, and not were asking to explain it; silly me.
Just did some research into -cz feminine nouns, I don't think only the last sound matters.
ta klacz - te klacze
ta rzecz - te rzecz
yta rozpacz - no plural
ta ciecz - te ciecze (I had to check it to be sure, it doesn't appear in plural too often)