Words that sound dirty but aren't.

Fartlek is a form of athletic training in which intervals of intensive and much less strenuous exercise are alternated in one long continuous workout. It literally means "speed-play" in Swedish.

Fuk was an old Middle English word for a sail, and in particular the foremost sail on a ship. A fukmast, ultimately, is a ship’s foremast, while the fuksheet or fuksail is the sail attached to the ship’s fukmast.

To grope a gull is an old Tudor English expression meaning "to take advantage of someone," or "to swindle an unsuspecting victim"—and a gullgroper does just that.

Taking its name from an Arabic word meaning "blustering" or "blowing," a haboob is a dry wind that blows across deserts, dustbowls, and other arid regions often at great speed, forming vast sandstorms as it goes. Haboobs are typically caused by the collapse of a cold front of air, which blasts dust and sediment up from the desert floor as it falls.

The Oxford English Dictionary calls a humpenscrump "a musical instrument of rude construction." Alongside others like humstrum, celestinette and wind-broach, it was originally another name for the hurdy-gurdy.

Invagination is simply the process of putting something inside something else (and in particular, a sword into a scabbard), or else is the proper name for turning something inside out. The opposite is called evagination.

Jaculation is the act of throwing or jostling something around, while to jaculate means "to rush or jolt forward suddenly."