It is preferable to hyphenate that word whether it is used as an adjective or a noun, but yearend -- one word -- is also acceptable. I always wait for the year-end sales to buy new furniture. I can't file my taxes yet because I am still waiting for my year-end documents.
Yes
No it doesn't require to be hyphenated.
It Is A Special Hyphen
Non-breaking hyphen
Nonbreaking Hyphen
If you're using the phrase as an adjective (example "I hate the end-of-the-year audit!") then it will definitely need the hyphens. Otherwise, the hyphens are incorrect.
A non breaking hyphen.
Yes, if you are using the phrase as an attributive adjective: 'She arranged the dominos on the table in an end-to-end pattern.' No, if you are using it as a predicative adjective or an adverb: 'The pattern that she chose for the arrangement was end to end.' 'She laid the dominos out on the table end to end.'
hyphen
A non-breaking hyphen is when you want two words to appear together on one line and not split over two lines. Once there is not enough space at the end of the line for the two words, both will be brought onto a new line, rather than having one on at the end of one line and the other at the start of the next line. So the two words and their hyphen are always kept as a single entity, and is therefore non-breaking. A non-breaking space works in the same way, always keeping two words that have a space between them on one line, like the name of a company.
No, the sentence should use a hyphen to connect "dead end" as a compound modifier: "He knew he had a dead-end job the first day he showed up for work."
As a noun they are two separate words. As an adjective you will use the hyphen.