Is "corrosion resistant material" incorrect?

When people say

They made the material corrosion resistant.

they mean corrosion resistant as an adjective. The word corrosion is only a noun, and resistant is both an adjective and a noun. But in this combination resistant isn't a noun, but an adjective.

The problem I have is that adjectives aren't formed as open Noun+Adjective forms. I think the correct form is corrosion-resistant. But people still write corrosion resistant without the hyphen.

So my question is: Is corrosion resistant without a hyphen correct or not? If it is correct, I would like to know why?

Solution 1:

In my opinion it should be written with a hyphen. The fact that it isn't does not necessarily change the meaning, just that someone has not seen fit to add a hyphen. But in a humanities department of a British university of which I am aware, such hyphenation is de rigeuer.

The NOUN-ADJECTIVE form is in everyday use; a light-sensitive cell, a man-eating tiger, an elephant-sized problem, a simple-minded idea etc.

Solution 2:

Rather than trot out rules-of-thumb (which certain institutions may of course make rigorous locally), one can try to find actual currency of usages. These Google ngrams

lend support to the claims that

1. the hyphenated compound is the more common form in attributive uses (~ 5 : 2)
2. the open form is the more common in predicative uses (~ 5 : 2)
3. all variants are used in significant numbers, making claims that some form is incorrect seem hyperprescriptive. The hyphen not being required to disambiguate, I'd go with this (though I'd choose to use the more common variants).