The short answer
According to SAYS, kopi O is black coffee with sugar, kosong means “nothing” and siu dai means less sugar. Kopi O kosong has neither sugar nor milk. Plain kopi needs another question: guides describe it differently. Ask the stall what goes in before you order.
Think of this as a counter-side cheat sheet. No spelling bee required.
SAYS and Wikipedia agree on kopi O and kopi O kosong. Their plain kopi descriptions differ. These are named guides’ descriptions, not one official dictionary for every counter.
| Word | What goes in the cup | Who says so |
|---|---|---|
| kopi | Condensed milk; separate sugar is not named. Wikipedia lists both sugar and condensed milk. | SAYS; Wikipedia |
| kopi O | Black coffee with sugar, no milk. | SAYS; malaysia4u |
| kopi C | Coffee with evaporated milk and sugar. | SAYS; KajoMag |
| kosong | Malay for “empty” or “nothing”; used for no sugar. KajoMag lists kopi C kosong as kopi C without sugar. | Wikipedia; SAYS; KajoMag |
| kopi O kosong | Black coffee without sugar or milk. | SAYS; Wikipedia |
| kopi kosong | Condensed milk, no added sugar. Only malaysia4u lists this order by name. | malaysia4u |
| siu dai / siew dai | Less sugar. Wikipedia’s coffee entry also names condensed milk. | SAYS; Wikipedia |
| kah dai / gah dai | Extra sugar; these sources spell it “gah dai”. | SAYS; Wikipedia |
| peng | Iced. SAYS lists milk, sugar and ice for kopi peng. | KajoMag; SAYS |
| gau / kau | Strong-brewed coffee with condensed milk; Penang’s “kau” means thick or rich. | SAYS ordering guide; SAYS Penang guide |
| poh | Weak-brewed coffee with condensed milk; Penang’s description is thin or diluted. | SAYS ordering guide; SAYS Penang guide |
| teh / teh O / teh C | Respectively: tea with condensed milk; tea with sugar; tea with evaporated milk and sugar. | SAYS |
| teh tarik | Tea with condensed milk, pulled between two cups to mix. | SAYS |
| kurang manis | Homage glosses it as “less sweet”, but does not define a cup recipe. | Homage |
malaysia4u is the only guide here that lists plain kopi kosong: condensed milk, no added sugar. SAYS and KajoMag list kosong only after O or C. Ask whether condensed milk stays.
Use the full name in the guide, then confirm anything uncertain.
SAYS gives kopi O kosong as coffee without sugar or milk. It separately gives kopi C kosong as coffee with evaporated milk but no sugar. Same ending, different milk description.
Ready-to-say orders:
“Kopi O kosong.”
“Kopi C kosong.”
SAYS defines siu dai as less sugar. Homage uses “less sweet” for kurang manis. The available sources do not establish that the two requests produce the same cup. The words are ordering shorthand; the uncle is not sitting an exam.
Makansutra gives two accounts: Carnation, the evaporated-milk brand, and coffee merchants association executive secretary Wee Jee Seng’s explanation that C comes from the Hainanese pronunciation of xian, meaning fresh.
Wikipedia also calls the origin uncertain. Both accounts point to evaporated milk. No need to settle the letter’s family history before ordering.
SAYS and Wikipedia describe black coffee without sugar or milk. Wikipedia traces O to Hokkien for black and kosong to Malay for empty.
Not in malaysia4u’s guide: its kopi kosong still has condensed milk, while kopi O kosong is black with no milk and no sugar. No other guide we found lists plain kopi kosong. Ask the stall which one it makes.
SAYS describes kopi C as coffee with evaporated milk and sugar, and kopi as coffee with condensed milk. Wikipedia lists sugar and condensed milk in plain kopi, and sugar and evaporated milk in kopi C. Both agree C means evaporated milk.