What is a good rule for the usage of the noun suffix -ment? Is desirement as acceptable as achievement?
-ment is not a free suffix you can add as you like. The nouns ending in -ment are either Latin or French. And the etymology of -ment is not clear. Even the meaning of -men and -mentum is difficult to analysize. If you study the Latin nouns in -men/mentum you find that the nouns are of various types and it is not possible to give a simple idea of the formation of these words. I could give my private view, but that would take too long and I think it would hardly help you.