Hello, I'm a language expert with a deep understanding of etymology and the historical development of words in various languages. Let's delve into the origins of the letter "M" as a symbol for a thousand.

In English, the use of the letter "M" to represent a thousand comes from the Latin word "mille," which means a thousand. This practice has its roots in the Roman numeral system, where letters were used to represent certain numerical values. The Roman numeral for 1,000 is "M," and this has been carried over into the way we denote large numbers in modern times.

The Latin word "mille" itself is derived from the Proto-Indo-European root "*ml̥to-," which is also the source of the English word "thousand." Over time, as languages evolved and numerical systems were standardized, the use of "M" for a thousand became a convention in many Western languages.

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The Roman numeral M is often used to indicate one thousand, and MM is used to indicate one million. For example, an expense of $60,000 might appear as $60M. Sales of $3,000,000 might be written as $3MM. Internet advertisers are familiar with CPM which is the cost per thousand impressions.read more >>