s

• 英语字母表的第十九个字母，为辅音字母，通常表示清齿龈擦音 /s/，也可浊化。它是英语中最常用的字母之一，用于构成复数形式和所有格。还可用作南方、小号、硫（化学元素）和秒（时间单位）的缩写。

The nineteenth letter of the English alphabet and the fifteenth consonant, representing the voiceless alveolar sibilant sound /s/ as in 'sun' or the voiced /z/ as in 'rose'. As a grapheme, 'S' is one of the most frequently used letters in English, crucial for forming plurals, possessives, and third-person singular verb conjugations. Its curved, serpentine shape resembles a snake. It functions as an abbreviation for south, small size, a symbol for sulfur in chemistry, a unit of time in seconds, and the nineteenth item in a sequence.

1. The nineteenth letter of the English alphabetA1formal

   The uppercase or lowercase character (S, s) that constitutes the nineteenth symbol in the Latin-based English alphabet, classified as a consonant. Its primary sound is a voiceless alveolar sibilant /s/, though it voices to /z/ in certain positions. It is the most common letter for forming plurals (cats, dogs) and possessives (John's). Its serpentine shape gives it the nickname 'the snake letter'.

   英语字母表的第十九个字母

   • The word 'sun' begins with the letter S.
   • Add an S to 'cat' to make it plural.
   • The hissing sound of S resembles a snake.
   • In the NATO phonetic alphabet, S is 'Sierra'.
   • The lowercase s curves like a ribbon in cursive writing.

2. An abbreviation for southA1formal

   The uppercase letter S used as the standard abbreviation for the cardinal direction south. It is found on compasses, maps, weather reports, and in regional designations. It is the opposite of N for north and is a fundamental element of geographic and navigational literacy.

   南（方向）

   • The compass needle points to N, so S is the opposite direction.
   • They migrated S for the winter.
   • The S side of the mountain gets more sun.
   • The map legend has N at the top and S at the bottom.
   • South Carolina is abbreviated SC, with S standing for South.

3. An abbreviation for small sizeA1informal

   The letter S used as a standard label in clothing, food, and product sizing to indicate a small size, typically representing the smallest option in a range of standard sizes. It is positioned below medium (M) and often has an extra-small (XS) variant. It is universally recognized in retail and service industries.

   小号（S）

   • I need a smaller size, please—this M is too big, do you have an S?
   • The coffee sizes are S, M, and L.
   • She always wears an S in designer dresses.
   • An S fries is perfect for a light snack.
   • The S bottle of water is 330 ml.

4. The symbol for sulfur in chemistryB1formalscientific

   The one-letter chemical symbol representing the element sulfur (or sulphur), atomic number 16. It is a bright yellow, non-metallic solid at room temperature. It is the tenth most abundant element in the universe and is essential for life, occurring in amino acids and many proteins. It is widely used in vulcanization of rubber, gunpowder, and sulfuric acid production.

   硫（化学元素）

   • Sulfur, symbolized by S, has a distinct yellow color.
   • Sulfuric acid (H₂SO₄) contains one S atom.
   • The rotten egg smell is due to hydrogen sulfide (H₂S).
   • S is an essential macronutrient for plants alongside N, P, and K.
   • Gunpowder is a mixture of charcoal, saltpeter, and S.

5. The abbreviation for seconds (time)A2formalscientific

   The lowercase letter s used as the international standard symbol for the second, the base unit of time in the International System of Units (SI). It is defined by the caesium-133 atomic clock. It is used globally in science, engineering, and everyday life for precise measurement of short time intervals and as a denominator in speed and frequency units.

   秒（时间单位）

   • The race was won in just 9.58 s.
   • The exposure time for the photograph was 1/1000 s.
   • The light turns red for 30 s before changing to green.
   • He ran the 40-yard dash in 4.5 s.
   • The SI base unit for time is the second, symbolized by s.