當

當 (Kangxi radical 102, 田+8, 13 strokes, cangjie input 火月口田 (FBRW), four-corner 9060₆, composition ⿱𫩠田)

• 儅(𰁸), 噹(当), 壋(垱), 㜭(𫰠), 擋(挡), 澢(𭰎), 檔(档), 璫(珰), 礑(𱳹), 襠(裆), 艡, 蟷(𬠅), 譡(𬣭), 鐺(铛)
• 劏(㓥), 㼕, 㽆, 簹(筜), 闣

• Kangxi Dictionary: page 764, character 18
• Dai Kanwa Jiten: character 21890
• Dae Jaweon: page 1175, character 9
• Hanyu Da Zidian (first edition): volume 4, page 2546, character 6
• Unihan data for U+7576

Historical forms of the character 當
Warring States	Shuowen Jiezi (compiled in Han)	Liushutong (compiled in Ming)
Chu slip and silk script	Small seal script	Transcribed ancient scripts

Phono-semantic compound (形聲 / 形声, OC *taːŋ, *taːŋs): phonetic 尚 (OC *djaŋ, *djaŋs) + semantic 田 (“field”) – fields facing each other.

當 (OC *taːŋs, “right; suitable; ought to”) (pronunciation 2) is the exopassive derivation of 當 (OC *taːŋ, “to have the value of; to be equal of; to face; vis-à-vis”) (pronunciation 1), literally "what is being matched".

黨 (OC *taːŋʔ, “class; party”) is the endoactive derivation of 當 (OC *taːŋ, “to be equal of”), literally "that which is equal in rank" (Schuessler, 2007).

Perhaps cognate with Tibetan དང (dang, “(together) with; and”) (Schuessler, 2007).

當

1. to face; to turn towards

   當面／当面  ―  dāngmiàn  ―  face-to-face

   當著眾人的面訓斥孩子 [MSC, trad.]
   当着众人的面训斥孩子 [MSC, simp.]

   dāng zhe zhòngrén de miàn xùnchì háizi

   to scold one's child in front of everyone

   • 當窗理雲鬢，對鏡帖花黃。 [Classical Chinese, trad.]
     当窗理云鬓，对镜帖花黄。 [Classical Chinese, simp.]

     From: 木蘭詩 (Ballad of Mulan)

     Dāng chuāng lǐ yúnbìn, duì jìng tiě huāhuáng.

     (please add an English translation of this usage example)

2. to bear; to withstand; to resist

   不敢當／不敢当  ―  bùgǎn dāng  ―  I really don't deserve this.

   當之無愧／当之无愧  ―  dāngzhīwúkuì  ―  to merit the reward; to be deserving

3. to undertake; to manage; to take charge of

   當權／当权  ―  dāngquán  ―  to hold power

4. to work as; to serve as

   讓我來當你的助手吧。 [MSC, trad.]
   让我来当你的助手吧。 [MSC, simp.]

   Ràng wǒ lái dāng nǐ de zhùshǒu ba.

   Let me be your assistant.

5. to match equally; to equal; to be equal to

   門當戶對／门当户对  ―  méndānghùduì  ―  to be well-matched in terms of socio-economic status (for purposes of marriage)

6. just at the time of; just happen (to be at a certain moment)

   當天／当天  ―  dāngtiān  ―  that day

   當我五歲時，我的母親突然得病身亡。 [MSC, trad.]
   当我五岁时，我的母亲突然得病身亡。 [MSC, simp.]

   Dāng wǒ wǔ suì shí, wǒ de mǔqīn tūrán débìng shēnwáng.

   When I was five, my mother suddenly fell ill and died.

7. just at (a place); at or in the very same

   當場／当场  ―  dāngchǎng  ―  on the spot

8. to meet; to happen to

   • 《易》之興也，其當殷之末世，周之盛德邪？當文王與紂之事邪？ [Pre-Classical Chinese, trad.]
     《易》之兴也，其当殷之末世，周之盛德邪？当文王与纣之事邪？ [Pre-Classical Chinese, simp.]

     From: I Ching, 11^th – 8^th century BCE

     “Yì” zhī xìng yě, qí dāng Yīn zhī mòshì, zhōu zhī shèngdé yé? Dāng Wénwáng yǔ zhòu zhī shì yé?

     Was it not in the last age of Yin, when the virtue of Gou had reached its highest point, and during the troubles between king Wen and (the tyrant) Gou, that the (study of the Yi) began to flourish?

9. (literary) still; to be

   • 雲長提華雄之頭，擲於地上，其酒當溫。 [MSC, trad.]
     云长提华雄之头，掷于地上，其酒当温。 [MSC, simp.]

     From: c. 1330 - 1400: Luo Guanzhong, Romance of the Three Kingdoms/Chapter 5

     Yúncháng tí Huá Xióng zhī tóu, zhì yú dìshàng, qí jiǔ dāng wēn.

     Yunchang's wine was still warm when he threw Hua Xiong's head on the ground.

10. to regard something/someone as; to think; to treat something/someone as
11. (literary) to make a judgement; to sentence
12. ought; should

    • 於諸侯之約，大王當王關中，關中民咸知之。 [Traditional Chinese poetry, trad.]
      于诸侯之约，大王当王关中，关中民咸知之。 [Traditional Chinese poetry, simp.]

      From: The Records of the Grand Historian, by Sima Qian, c. 91 BCE

      Yú zhūhóu zhī yuē, dàwáng dāng wàng Guānzhōng, Guānzhōng mín xián zhī zhī.

      By the covenant made with vassals, you should be the king in Guanzhong; all people of Guanzhong knew this.

    • 言亂極當治，天必將使夫子得位設教，不久失位也。 [Written Vernacular Chinese, trad.]
      言乱极当治，天必将使夫子得位设教，不久失位也。 [Written Vernacular Chinese, simp.]

      From: Various editors, Collected Conversations of Master Zhu, c. 13^th century CE

      Yán luàn jí dāng chí, tiān bì jiāng shǐ fūzǐ déwèi shèjiào, bùjiǔ shī wèi yě.

      (please add an English translation of this usage example)

13. gap; space; break
14. a surname

• (still): 尚 (shàng), 還／还 (huán)
• (ought to):

• → Vietnamese: đang (present tense marker)

當

1. to match; to be equal to
2. (obsolete) to lead; to manage
3. proper; suitable; adequate; fitting; appropriate

   恰當／恰当  ―  qiàdāng  ―  appropriate

4. to regard as; to consider as; to treat as

   把寵物當自己的孩子養 [MSC, trad.]
   把宠物当自己的孩子养 [MSC, simp.]

   bǎ chǒngwù dàng zìjǐ de háizi yǎng

   to raise one's pets like one's children

   你從不把我當自己人。 [MSC, trad.]
   你从不把我当自己人。 [MSC, simp.]

   Nǐ cóngbù bǎ wǒ dàng zìjǐrén.

   You never treat me like one of your own.

5. to think

   你真當我不知道麼？ [MSC, trad.]
   你真当我不知道么？ [MSC, simp.]

   Nǐ zhēn dàng wǒ bù zhīdào me?

   You really think I don't know?

6. to pawn; to put in pawn

   當了手錶／当了手表  ―  dàng le shǒubiǎo  ―  to have pawned a watch

7. pawn; something pawned
8. pawnshop (often used in names of pawnshops)
9. trick; fraud; deception

   上當／上当  ―  shàngdāng  ―  to be taken in

10. (Taiwan, slang, of teachers or professors) to fail someone

• → Vietnamese: đáng (“worthy; to deserve”)
• → Zhuang: dangq (“to pawn; to be the same as; to treat as”)

擋 (OC *taːŋʔ, *taːŋs, “to block; to obstruct”) is a derivative and was originally also written as 當 (Wang, 1982).

當

1. Alternative form of 擋 / 挡 (“to block; to obstruct”)

   螳臂當車／螳臂当车  ―  tángbìdāngchē  ―  to overrate oneself and try to hold back an overwhelming force

   • 一身轉戰三千里，一劍曾當百萬師。 [Classical Chinese, trad.]
     一身转战三千里，一剑曾当百万师。 [Classical Chinese, simp.]

     From: 8th century, Wang Wei, 老將行

     Yīshēn zhuǎnzhàn sānqiān lǐ, yī jiàn céng dāng bǎiwàn shī.

     (please add an English translation of this usage example)

當

1. the same (day etc.)

   當天／当天  ―  dàngtiān  ―  that very day