Rule for masculine · der
-ismus → der · 0.1%, no exceptions
Nouns borrowed from Greek or Latin that end in -ismus are almost always masculine, just like their English "-ism" cousins. It's a rare pattern in our set - only 3 words out of 2,400 - but a very safe one: we found zero exceptions. You'll recognize it in words like der Tourismus, der Rassismus, and der Antisemitismus; when a plural exists, it's formed with -ismen (e.g. Rassismen). If you meet a new word ending in -ismus, you can bet on der with confidence.