Parents tell children to mind their manners. People tell each other to mind their own business. “Mind” is a versatile verb that means “pay attention to.” By way of contrast, “never mind” is an expression that means “do not pay attention to.” However, did you know that the meaning of “never mind” is different from the meaning of “nevermind”? If you were unaware that “nevermind” can be spelled with or without a space, it’s understandable. You can’t hear the space, but it does make a difference.
Around the late 1700s, the expression “never mind it” arose. The function of the phrase was to tell people not to worry about something or not to trouble themselves. For example, if a child accidentally spilled a glass of water, the mother might reply “Never mind it, child; it’s just water.” Later, the expression was truncated to “never mind.”
In the above example, “never mind,” written as two words, functions as a verb. As you can imagine, the phrase has evolved in the hundreds of years since 1795. Now, “never mind” often appears as a mere interjection. When a speaker says something that is unimportant, she may say “never mind” instead of repeating or explaining what she just said. A speaker might also use the phrase when he changes his mind. “Bring me a piece of chocolate cake. No, never mind! I’d better stick to my diet.” In that case, the meaning is closer to “forget it.” The American Heritage Dictionary of Idioms reveals another usage of never mind. It can mean “not to mention” or “and certainly not”: “I can’t imagine getting married, never mind having children.”
What if there is no space between the two words? Dictionary.com lists “nevermind” as a noun with a note. Try to guess what the note is, based on these two examples:
Those dastardly scoundrels aren’t worth your time, Gladys. Pay them no nevermind.
Don’t ask so many questions. What Gladys does with her time is no nevermind of yours.
In the first sentence, “nevermind” means “attention or notice.” Gladys shouldn’t give any attention to the scoundrels. In the second example, “nevermind” means “business or responsibility.” You could easily replace “nevermind” with “business.” It becomes apparent that both examples are idiomatic when you try to use “nevermind” in an affirmative context.
Pay nevermind to your friends; they miss you!
Tell your daughter how you feel; her business is your nevermind.
Neither example makes sense, does it? Did you guess what was in the note? Dictionary.com classified both of these noun definitions as older uses. The Oxford English Dictionary classifies it as regional. The Merriam Webster and American Heritage dictionaries don’t accept it at all! And it’s true; it’s unlikely that you would hear anyone using “nevermind” in either of these contexts today. Therefore even if it’s a part of your vocabulary, it is not advisable to use it in any formal context.
Nevermind means “a matter of importance” or “attention.”
Don’t use “nevermind” in formal contexts.
“Never mind” tells someone to disregard a matter. It can also mean “not to mention” or “certainly not.”
Children should mind their parents. People should probably mind their own business too. In fact, there are a lot of important things you should pay attention to in life. You can always dismiss the inconsequential things with “never mind,” or use the phrase to indicate a change of heart. If you use it without a space, remember that it is a noun meaning attention, notice, or responsibility.
from Grammarly Blog https://www.grammarly.com/blog/how-to-use-nevermind-correctly/