[desert_boi]

Since enormous is from Latin, stems tend to be Latin. `ness` generally only is morphologically productive with Germanic roots, kindness, happiness, etc.

When I visited Iceland, I remember a sign in English that said a cliff was insafe [sic]. `in` being a Latin morpheme, and safe being Germanic.

[riffraff]

Ah, I never realized in/un would be used with corresponding Latin/Germanic words.

But then, it seems there are quite a few un+latin (unreal, unbalanced, unadulterated, uncertain etc), even if I can't think of in+Germanic.

[desert_boi]

Good counter examples. Etymonline will break roots down for you.

https://www.etymonline.com/word/unbalanced#etymonline_v_2490...

Like most things in linguistics, the 'rules' are more a rule of thumb than the mathimatical sort.

Germanic pre/post fixes seem like they stick to pre-inkhorn roots better.

https://en.wikipedia.org/wiki/Inkhorn_term