How was your trip?

[m.ellis]

That would be me, I'm afraid. I know the correct derivation from Latin is Terragens, but I happen to prefer terragen. The 'gens' ending sounds like a plural noun, when I want to use it as an adjective (the Terragen Sphere).

The genitive form would be Terragentis.

It is quite common for words created in one language from pieces found in another to suffer a bit of grammatical 'breakage' on the journey, especially if the part that breaks off is something that simply didn't 'fit' well with usage in the new context (like the example Steve gives). This is certainly true of many words that are now part of English, and yes, it makes purists wince unless the adoption is so ancient that everyone has forgotten it. If we want to get into it, we can always suppose that 'Terragen' is not directly from Latin but was imported whole from some Latin-derived language.

What do our linguists think of this?

Language borrowing tends to be sloppy. For example, the military ranks Lieutenant General, Major General, and Sergeant-Major were originally, in French and Spanish,
General Lieutenant, General Major Sergeant, and Major Sergeant. We English-speaking types turned nouns into adjectives and adjectives into nouns.

Anyway, I'm fine with using Terragen as long as it's a conscious decision and not just the product of error. (Yeah, I'm feeling magnanimous today.)