Samuel Wells Williams (1812-1884), known as Wèi Sānwèi 衛三畏 in Chinese (Wei 衛 is a surname), was an American missionary, diplomat, and sinologist.

After a productive 40 years spent in China, Williams returned to the United States in 1877 and became the first Professor of Chinese language and literature at Yale University.

Williams' (1856) A Tonic Dictionary of the Chinese Language in the Canton Dialect[7] or ˌYing ˌWá ˌFan Wanˈ Ts'ütˌ Lúˈ 英華分韻提要 ("English-Chinese Summary of Tonal Divisions") includes 7,850 characters commonly used in Cantonese.

[9] Williams began compilation in 1863, when he was chargé d'affaires for the United States in Beijing, and after realizing that foreigners required more than a wordlist of common Chinese terms, he decided to produce a successor to Morrison's dictionary.

[7] Although he said, "Dr. Medhurst's translation of the K'anghi Tsz'tien"[13] has been much used", the principal source for definitions was the original Kangxi zidian, which "imperfect as it is according to our ideas of a lexicon, is still the most convenient work of the kind in the language".

The plan of a Chinese lexicon to satisfy all the needs of a foreigner, should comprise the general and vernacular pronunciations, with the tones used in various places, and the sounds given to each character as its meanings vary.

But even when arranged and ready, the foreigner would find it to be incomplete for all his purposes by reason of the local usages, ...[15] Yong and Peng interpret this desideratum as Williams' explanation for including regional pronunciation variants in A Syllabic Dictionary, and say, "As good as his intention was, it was highly doubtful whether he could achieve his goal.".

[18] After thieves stole 250 stereotype printing plates of the dictionary from the Mission House in 1879, Williams made corrections and additions for the revised pages, which were used in a new 1881 edition.

[24] Williams' dictionary represents the four tones in the same uncommon method as his Easy Lessons in Chinese:[4] semicircles written in one of the four corners of a character (the linguistic term fāngkuàizì 方塊字, lit.

[23] The Chinese character 道 for dào "way; path; say; the Dao" or dǎo "guide; lead; conduct; instruct; direct" (or 導 clarified with Radical 41 寸 "thumb; inch") is a good litmus test for a dictionary because it has two pronunciations and complex semantics.

A road, path, or way; in geography, a zone or belt; in medicine, anal and urinal passages; a circuit; the officer who oversees a circuit or region; a principle, a doctrine, that which the mind approves; and used in the classics in the sense of the right path in which one ought to go, either in ruling or observing rules; rectitude or right reason; in early times up to A. D. 500, the Buddhists called themselves |人 men [seeking for] reason or intelligent men, denoting thereby their aspirations after pu-ti (Sanscrit, boddhi) intelligence; the Reason or Logos of the Rationalists, denoting an emanation, the unknown factor or principle of nature, the way it acts in matter and mind; to lead; to direct, to follow out; to go in a designated path; to speak, to talk, to converse; as a preposition, by, from; the way or cause a thing comes; a classifier of courses at a feast, edicts and dispatches, gateways, walls, rivers, bridges, &c.; a coating, a layer.

[25]The entry's 39 word and usage examples—which use Morrison's "|" abbreviation for the head character 道—include common expressions (bùzhīdào 不知道 "I don't know", dàolù 道路 "a way; a road"), Chinese Christian expressions (zìgǔdào 自古道 "as saith the proverb"), Chinese Buddhist terms (dédào 得道 "to become perfect and enter nirvana; used by Buddhists [sic]"), and literary set phrases (Dàoxīn wéi wēi 道心惟微 "the principle of right in the heart is small" comes from the Book of Documents contrasting the 人心 "human heart-mind" and the 道心 "Way's heart-mind": "The mind of man is restless, prone (to err); its affinity to what is right is small".

[31] The British consular officer and linguist Herbert Giles published a 40-page brochure On some Translations and Mistranslations in Dr. Williams’ Syllabic Dictionary, saying that it is "though in many ways an improvement upon its predecessors, is still unlikely to hold the fort for any indefinitely long period".

[35] Censuring Williams' dictionary for transliterating pronunciation from a "general average" of regional variants rather than Peking pronunciation, James Acheson wrote an index arranged according to Thomas Francis Wade's orthography,[36] citing the frustration that many dictionary users who after "repeated failures to find the commonest characters without reference to the radical index or, failing here as often happens, to the List of Difficult Characters".