I was ready to chime in agreeing with those who have said it's not a word, but first I ran a search for the term and the first two results were Cambridge defining it and Merriam-Webster offering synonyms for it. So, we've established that it is indeed a word. But to answer the question of how often it is used: I would have to say the best answer is almost never.

I use "simultaneity." But "simultaneousness" is used. Why do I think it is used? I was pretty sure it was. However, I checked an English dictionary, and you should get in the habit of doing that, too. I don't mean a Polish-English dictionary, I mean a single-language English dictionary. My personal favorite is ahdictionary, the American Heritage dictionary, online. It lists "simultaneousness." It also mentions "simultaneity" as equivalent. It's NOT a word you need to use often! Here's one example. "According to Einstein's theory, it is impossible to tell whether two distant events are simultaneous or not. It destroys the concept of simultaneousness." "

Hi :), I have a question, is the word "simultaneousness" used in English language? And if so, how often and could you give me an exaple in a sentence? I came across this word, when I was checking the meaning of "simultaneous" and "simultaneously" Hi Daria, In all my life - over 50 years of being a native English speaker - I have never heard of the word: simultaneousNESS! The words simultaneous and simultaneously exist and are used. The word simultaneity also exists. I had to look up the word simultaneousNESS in my Oxford compact English dictionary but it was not listed! To the best of my knowledge this word does not exist; at least not in British English! Maybe one of our American friends here could confirm if such a word exists. It may exist in American English because I believe that they follow different rules of grammar and spelling. For example, in British English we write: I practiSe Spanish every day. but, The dental practiCe opposite my house is always very busy. We use the letter S when we write the verb but we use the letter C when we write the noun. I hope this helps 😀

Here are some examples of use. Again, this is NOT a common word. I suggest that you do NOT try to use it. If you need to express the idea, I suggest that you find a simpler way to express it. I found these in search of Project Gutenberg, contains books out of copyright and thus mostly from before 1923. These were times when writers used formal English, complicated grammar, and advanced vocabulary. In the novel "Moby-Dick," by Herman Melville, dangerous things are all happening at the same time, and he writes about the "wild simultaneousness of a thousand concreted perils..." In an (obscure!) novel by Jack London, a character in the novel writes: "I resent your development if it is because of it that you speak prosaically of a prosaic marriage and of a honeymoon simultaneous with the Degree. I think you are too well pleased with the simultaneousness." Another writer says "We see often in the world's history a simultaneousness in the regeneration of thought." In other words: there is a tendency for people to get the same ideas simultaneously. That tendency is "simultaneousness." "the boys, to the best of their knowledge and ability, bowed to him, and the girls, with an attempt at simultaneousness, dropped [curtesies] of respect." The "attempt at simultaneousness" means they both tried to curtesy in synchronization, at the exact same time. "each lowered his cigar suddenly with the simultaneousness of a drill." The writer means a military drill. In a military drill, soldiers try to perform some action, like shouldering a rifle, simultaneously. The men's actions with the cigars had the same "simultaneousness" as a military drill.

Dan provided a good answer. He often does. The use of the word simultaneousness is very rare just like one of its synonyms contemporaneousness. They're not used in day-to-day writing and/or conversations for the most part.