Rule for feminine · die
-heit → die · 0.8%
The suffix -heit builds feminine abstract nouns (die), usually from an adjective: die Sicherheit (safety, from "sicher"), die Mehrheit (majority, from "mehr"), or die Vergangenheit (the past, from "vergangen"). It's a small but perfectly reliable pattern - among our 2,400-word list, all 20 nouns ending in -heit are feminine, with zero exceptions. So you can learn it with confidence: almost any new word you meet ending in -heit will be die.