tenet

First recorded in 1590–1600; from Latin: “he holds,” 3rd person singular present indicative of tenēre “to hold”; cf. tenant

The word tenet is often mispronounced as [ten-uhnt], /ˈtɛn ənt/, with an extra /n/ sound in the second syllable—exactly like the word tenant (meaning someone who rents and occupies an apartment, office, etc.). It is a mistake made by people across a wide range of educational backgrounds, because it is such a natural one to make: English has thousands of words that end in the unstressed syllable -ant or -ent, such as parent, accident, potent, and relevant. Moreover, the two sounds at the end of all these words—/n/ and /t/—are very easily made together because we pronounce them with the tongue in the same place, touching the upper palate (or roof) of the mouth. The almost identical-sounding and common word tenant makes it all too easy for the extra /n/ to creep into the second syllable of tenet.
Another word that is liable to be mispronounced in a similar way, with an extra /n/ in the second syllable, is pundit. No doubt the first /n/ in both tenet and pundit also influences their mispronunciation. And in pundit, the /d/ sound is another one made in the same place as both /n/ and /t/. Talk about piling on!

C17: from Latin, literally: he (it) holds, from tenēre to hold