Here are the meanings of the least-found words that were used in (mostly) recent Times articles.

1. tritium — a radioactive form of hydrogen used in nuclear weapons:

With this kind of nuclear waste, I’m not referring to water containing the radioisotope tritium that nuclear plants regularly release. — Nuclear Waste Is Misunderstood (April 28, 2023)

2. ennead — a group of nine:

The remaining nine partners wanted to more accurately signify their collaborative process. Ennead (pronounced EN-ee-ad) denotes a group of nine deities in Egyptian mythology. — Architecture Now Building New Names (Sept. 29, 2010)

3. wahine — a Polynesian woman or a female surfer:

And I wasn’t the only smitten wahine. Over the past four years, the number of girls and women surfing regularly has increased 280 percent, according to the Surf Industry Manufacturers Association. — Women and Surfing Are an Endless Combination (Aug. 30, 2003)

4. tomtit — any of several small songbirds (and a regular Spelling Bee stumper):

The Audubon Society would file a complaint in defense of tomtit virility. But, such is the state of Massenet’s reputation, I doubt that many sophisticated operagoers would rush to defend him. They have been made to feel shame for too long. — Music View: Massenet — Minor but Significant (Aug. 3, 1986)

5. mammon — wealth that has a corrupting influence:

One easy take — which I predict will be heard in houses of worship this coming weekend — is that Americans need to return to traditional values and forsake the glorification of mammon. — Money Is Up. Patriotism and Religion Are Down. (March 29, 2023)

6. monomania — excessive focus on a single thing:

The manifesto reads like a bullet-pointed pep talk. Some of her points are tongue-in-cheek — “When in doubt spray-paint it gold” — while others are universal: “Fight monomania,” and “Wake up early, fear death.” — In Los Angeles, Rebecca Morris and Peter Bradley’s Art ‘About Nothing’ (Nov. 3, 2022)

7. adenine — one of the four bases of DNA:

Huntington’s is a hereditary neurodegenerative disease caused by excess repetitions of three building blocks of DNA — cytosine, adenine and guanine — on a gene called huntingtin. — Sought Out by Science, and Then Forgotten (May 23, 2023)

8. tippet — a long piece of cloth often worn over the shoulders; or, in fishing, a line that connects the leader to the fly:

“I quickly raised my rod, hoping I would not snap the 5X tippet against his moving weight.” But then, he wrote, the fish fought back, “his broad red side glistened in the glow of the setting sun. — Dave Whitlock, a Star of the Fly-Fishing World, Dies at 88 (Dec. 29, 2022)

9. pipit — a type of small, often brown, ground-nesting songbird found throughout the world:

Rats and mice also accompanied the sealers and whalers. Rats in particular found plenty of bird eggs and chicks to feed on, including those of two endemic species: the South Georgia pintail, a small duck; and the South Georgia pipit, the island’s only songbird. These birds were literally swallowed up — and their songs vanished, too. — Abundance, Exploitation, Recovery: A Portrait of South Georgia (April 18, 2022)

10. natant — swimming or floating:

I love the word natant. The fact that it means “swimming or floating” makes me want to connect it somehow to the word “natal” because a fetus floats, but “natal” is apparently derived from the Latin natalis, meaning “pertaining to birth or origin.” — A Season in the Sun (April 28, 2017)

And the list of the week’s easiest words: