Warning: You will never look at lemurs the same way again. This one's for linguaphiles and lemurphobes alike.
Fizzle
Back in the 17th century when people didn't have cell phones and essentially had nothing to do except talk about farting, "Fizzle" meant to break wind without making a noise. The word comes from the Old English fisting, which means farting, and it's totally related to our word "Feisty," which, weird.
"Kibosh"
The prevailing theory is that "kibosh," as in "to put the kibosh on something," comes from the Gaelic cie bais, which means "cap of death," a thing executioners used to put on in the mornings so as to look more badass and terrifying when they killed people. Let's all agree never to say "kibosh" again.
Vagina
Vagina is Latin for sheath. Feminism hadn't been invented when they came up with that one.
Penguin
"Penguin" comes from the Welsh pen meaning "head" and gwyn meaning "white." The Welsh person who came up with this one wasn't blind — he or she was just referring to the great auk, now extinct. RIP, the great auk, with your beautiful white head. I am sad now.