By happenstance, I stumbled upon the words cha, char and chai in the dictionary today, all defined as meaning tea in informal British English. I lived and worked in London for some time, but never heard it used, so I am wondering: is it specific to certain dialects? Or is it dated? The Oxford English Dictionary doesn't mention anything like that.
"Char" is an old British English (in fact I would say English English) slang term for "tea". I don't think it is heard particularly often, but you might see or hear the phrase "cup of char and a wad" (meaning "cup of tea and a slice of cake") in a WWII context for example.
I seem to recall that Reggie Perrin used this expression in David Nobbs' novel 'The Fall and Rise of Reginald Perrin' back in the 1970s, but even then the café waitress didn't understand it and he had to translate. So I think it is a fairly rare beast, and probably often used (as in Reggie's case) to sound deliberately working class or for humourous effect.
Chai, or its variants, are terms borrowed from various Asian languages, meaning "tea". Wikipedia, citing the AHD, gives the Mandarin chá (茶) as origin, then transmitted to Persian چای, and subsequently to other languages (e.g.: Hindi: चाय cāy, Urdu: چاۓ , cāy, Marathi: चहा cahā, Gujarati ચા chā, Bengali: চা cha).
The OED says that chai is generally used as shorthand for Masala chai, literally spiced tea, a tea made by brewing tea with a mix of spices in milk. Often you will also hear it called chai tea which, I guess, is a bit redundant... or, especially in the US, chai latte (see definition below), which is, again, redundant.
chai Mil. slang.
Any of various specific preparations of tea (typically associated with countries or regions where chai is the generic word for tea). Now esp. = masala chai n. at masala n. Compounds.
chai latte n. orig. N. Amer. a hot drink similar to masala chai, made with spiced tea (or a commercially produced concentrate) and steamed milk.
As for the regionality of the term, I can't help. I heard it commonly when I was living in NZ, don't know how widespread is in the UK or USA.
Indeed, most languages in the world use a variant of cha. This goes back to the continental Chinese word (茶 chá). In the pictogram, you can distinguish the grass radical (艸) on top of the plant itself complete with roots and leaves.
- The Japanese took the name, the thing and the character from Chinese (when Japanese borrows only the Chinese Hanzi (漢字) character it is pronounced with the original Japanese name different from the Chinese monosyllabic pronunciation).
- In Russian (Чай) and Romanian (Ceai) it is also pronounced "chaï".
- In Portuguese it is "chá" as well.
- Greek (Τσάι - tsai)
- In Classical Arabic as well.
- Indian dialects as shown by @nico comply with the universal pronunciation.
In reality very few languages use tea/thé/tè/té (English, French, Italian/ Spanish and maybe a few others).
The most well known area where Chinese tea is grown is Fujian (福建) in front of Taiwan and in the dialects spoken over there (閩語 - Mǐn yǔ or simply Mǐn), in contrast to Cantonese and Mandarin, the character 茶 is pronounced "teey". Hence our tea.
Going back to the dictionary entry, one possibility is that the increasing cosmopolitanism of England and the US are the cause of this new loanword.
It may be useful to examine the derivation of the word tea itself. According to Etymonline.com:
tea 1650s, earlier chaa (1590s, from Port. cha), from Malay teh and directly from Chinese (Amoy dialect) t'e, in Mandarin ch'a. The distribution of the different forms of the word reflects the spread of use of the beverage.
Regarding the "distribution of the different forms" I can add this data point: In Japanese the word for tea is cha (茶), usually rendered politely in conversation as お茶 (o-cha, or "honorable" tea). This was obviously borrowed from the Hanzi.
According to Paul Irving
Although it's rare now, 'char' used to be in common use in England, at least among the working class. It was brought back by soldiers who'd served in India. I remember it from my childhood.
4 char (tʃɑː ) noun
(British) a slang word for tea
Word Origin from Chinese ch'a