It is written as two words if used as a noun: "he entered the house through the back door." It is written as one if used as an adjective: "the Basketball team ran a backdoor play that produced an easy layup."
2.105 is written as: two and one hundred five thousandths.
This number is written as: six quintillion two hundred eighty-one quadrillion
One word, two syllables
Literally, "Zero point six nine two." As a fraction, "Six hundred ninety-two one-thousandths."
The word form is: two hundred octovigintillion.
The word "hairbrush" is typically written as one word, not two.
"Nosecone" is typically considered to be one word. It refers to the pointy, usually cone-shaped structure at the front of certain vehicles or objects, like aircraft or rockets.
It is one word.
The word "underfund" is typically written as one word.
It is one word.
It is usually written as one word.
"Wheelchair" is typically written as one word.
newsletter is a compound word
It can be written as one word or two or as a hyphenated word, all are correct.
Businessmen is often written as one word. It can be two words or even hyphenated
"Weatherman" is typically written as one word.
Underdeveloped should be written as one word, not two words or hyphenated. I hope this answered your question. :)