I am trying to find alternative ways to refer to a very necessary thing or thing that someone must have. Can I use the word needful for this purpose? A person said that needful means the thing needs something but not that somebody needs it.
I will only offer this data point: In 1991, best-selling author Stephen King published a novel (later made into a movie), called Needful Things. From the Wikipedia entry:
It is obvious that the meaning of needful in this title is not "things that are needy" but "things that people think they really need" (i.e., that they find necessary and feel they simply have to possess).
Now, I will agree in advance that this usage is a bit formal and obscure, with an air of the rural or rustic about it, and that it is not in common usage. Nevertheless, the fact that a best-selling author can use the word in the title of a popular novel suggests that the word is not so obscure that people will not understand it.
There are plenty of little-used words that native speakers understand without using themselves. This brings up the question of what constitutes usage. If everyone understands a word, that seems to me to be evidence that the word is common even if it is rarely spoken. How often do we use words like "umbrage"? Rarely, if ever. Yet when they come up we know exactly what they mean. That feels to me like some form of currency.
Merriam-Webster lists two meanings for the adjective needful: being in need and necessary, requisite. It also lists two meanings for the noun needful: something needed or requisite and money.