Are all twenty of these words valid in Scrabble?

Most are valid in the Tournament Word List (TWL). A handful (PETRICHOR, DEFENESTRATE, JAZZBO, ZUGZWANG) are too long or contain repeated letters that make them impossible or unplayable in a standard Scrabble game — they are on the list for their value in writing.

Which of these words do you actually use in everyday writing?

PETRICHOR, QUOTIDIAN, DEFENESTRATE and SUSURRUS all show up regularly in published prose. The rest are word-game specialists.

Are these words valid in Words With Friends?

Most are. The WWF dictionary overlaps heavily with Scrabble but adds newer entries — see the WWF dictionary article for exact differences.

How many of these should I try to learn at once?

Three per week is realistic. Twenty at once means you will remember none in a month.

Rare English Words Worth Knowing (and Playing)

There is a whole genre of "rare word" list posts full of nineteenth-century curiosities like BORBORYGMUS that nobody will ever use in conversation and that don't help you in a word game either. This list is different. Every word here earns its place on at least two grounds: it is playable in Scrabble or WWF and it is either genuinely useful in writing or teaches you something about English structure. Where relevant, we note the Scrabble tile score.

The twenty

1. QOPH (18 points, Scrabble)

The nineteenth letter of the Hebrew alphabet. A perfect Q-without-U word. Q(10) + O(1) + P(3) + H(4) = 18 raw, but on a plain lane it scores 18 without premiums. Its value in play: it uses the Q on a rack that has no U. See Q without U: the complete list and how to play them.

2. ZAX (19 points)

A tool for cutting roof slates. Three letters, two of them power tiles. Z(10) + A(1) + X(8) = 19. In writing, useless. On the board, worth learning because Z and X land on your rack together more often than you would guess.

3. AECIUM (10 points)

A cup-shaped structure in fungi that produces spores. Six letters, five of them vowels. This is a vowel-dump lifesaver: A(1) + E(1) + C(3) + I(1) + U(1) + M(3) = 10. If your rack is AEEIOUM you play AECIUM and thank the mycologists.

4. PETRICHOR

The smell of earth after rain. Ten letters, so unplayable in a normal Scrabble turn, but it has entered common English writing since about 2015. Worth knowing simply because you will read it. Coined 1964 by two Australian scientists.

5. SPRAUNCY

Smart-looking, dapper. British informal. Eight letters, playable across a triple-word for serious points. S(1) + P(3) + R(1) + A(1) + U(1) + N(1) + C(3) + Y(4) = 15. Also just a wonderful adjective.

6. ZUGZWANG

A chess position where any move worsens your position. Now common in strategy writing generally. Contains two Zs — impossible in standard Scrabble which has only one Z tile, so a great trivia entry.

7. GOAF

The waste material left in a mined-out area. Four letters, useful when you have a G and an F and a spare vowel.

8. QI (11 points)

The two-letter powerhouse. Life force in Chinese philosophy. Q(10) + I(1) = 11 raw. On a double-letter under the Q it becomes 21, on a double-word 22. Learn it. See the 124 two-letter Scrabble words ranked by usefulness.

9. XI (9 points)

The fourteenth letter of the Greek alphabet. Cousin to QI in Scrabble utility.

10. SUSURRUS

A whispering or rustling sound. Genuinely useful in writing. Eight letters, plays across a triple-word lane. S(1) + U(1) + S(1) + U(1) + R(1) + R(1) + U(1) + S(1) = 8. Not high-scoring but memorable.

11. AECIA

Plural of aecium. See #3.

12. TSKTSK / TSKTSKS

Yes, both are valid in Scrabble. Interjection of disapproval. Learn for the shock value.

13. MUUMUU

A loose dress. Six letters, four of them U. The ultimate U-dump. M(3) + U(1) + U(1) + M(3) + U(1) + U(1) = 10.

14. CWM

A steep-walled valley (Welsh loanword, common in geography). Three letters, no vowel. C(3) + W(4) + M(3) = 10. Useful when your rack has too many consonants.

15. DEFENESTRATE

To throw someone out of a window. Twelve letters, unplayable in Scrabble. But this is a word that pays off in writing every time you use it correctly.

16. ZLOTY (17 points)

The Polish currency unit. Z(10) + L(1) + O(1) + T(1) + Y(4) = 17 raw; regularly a triple-word bomb.

17. JAZZBO (33 points raw; J8 + A1 + Z10 + Z10 + B3 + O1)

A person who loves jazz. Contains two Zs — again a trivia note, since standard Scrabble has one Z, so this is unplayable in a normal game.

18. NGWEE

A monetary unit of Zambia. Five letters, no vowels in the traditional sense (W acts vowel-like here). N(1) + G(2) + W(4) + E(1) + E(1) = 9. A rack-saver when you draw NNWWE.

19. PSHAW

Interjection of contempt. Five letters, valid. P(3) + S(1) + H(4) + A(1) + W(4) = 13. Also perfectly usable in dialogue.

20. QUOTIDIAN

Daily, ordinary. Nine letters, playable across a triple-word for a big score. Q(10) + U(1) + O(1) + T(1) + I(1) + D(2) + I(1) + A(1) + N(1) = 19 raw. And unlike most Q-words, this one is a genuinely elegant piece of English worth using in prose.

How to actually learn these

Reading a list once does nothing. Play three of them into your next Scrabble or WWF game. Two weeks later you will still know those three. The other seventeen will fade. This is the pattern for every rare-word list you will ever encounter, and the reason word games teach vocabulary better than flashcards.

If you want to work systematically through low-frequency words that also score, the words containing q, words containing x and words containing z pages are dense with candidates. Pick five you don't know per week and play at least one.

The point of rare words

Rare words are not decoration. Each one you know is a small compression: PETRICHOR replaces "the smell of earth after rain," QUOTIDIAN replaces "occurring daily as a matter of course," DEFENESTRATE replaces "to throw someone out of a window." Precision is efficient. In word games, precision also scores. The two goals — write better and play better — align surprisingly often, and this list is where they overlap.