As a linguistic expert with a deep understanding of the evolution of language and its usage, I can provide an explanation for why we say "K" for thousand.

In English, the practice of using "K" as an abbreviation for "thousand" is derived from the Greek word "χίλιοι" (pronounced khilioi), which means a thousand. This word is often represented by the letter "K" in Roman numerals, which is a system of notation that originated from the Roman Empire. The Roman numeral for 1,000 is "M," but for smaller multiples of 1,000, such as 5,000, they used "D" for 500 and then added a horizontal line over it to indicate ten times that amount, which is "V̅" (5,000). However, for 1,000, they used the letter "C" for 100 and added a bar over it to indicate ten times that amount, which is "X̅" (1,000). Over time, the bar was dropped, and the letter "K" came to be used as a shorthand for "thousand" in English, especially in financial and scientific contexts.

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To minimize confusion I would stick with K for a thousand. K comes form the Greek kilo which means a thousand. In the metric system lower case k designates kilo as in kg for kilogram, a thousand grams. Even here there is some ambiguity.read more >>