words on ous
Above site gives most of all existing words ending on ous.

In stead of always asking I've found my way to find things since I came here almost two years ago.
A continuing problem though is 'words ending on ous'.
There are those on ous, eous, ious and uous. Most of the time I have to double check if I've done it right. Is there a memory help or a system for this matter?

f.i.: with aeneous and acrogenous both following an n, one is :eous , the other ous. (?)

You're asking for something logical like a system? In English?
I think you just have to remember them.
I don't think I've ever used either of the examples you give.

My guess would be that the suffix is -ous and it is invariant. Any vowels that immediately precede the -ous are part of the root.

I looked up the origin of igneous, and found:
igneous
1664, from L. igneus "of fire, fiery," from ignis "fire," from PIE *egni- (cf. Skt. agnih "fire, sacrificial fire," O.C.S. ogni, Lith. ugnis "fire").
the "other" OED
I don't know what O.C.S. is, but that seems to verify Faldage's idea.

I don't know what O.C.S. is

It's Old Church Slavonic (sometimes called Old Bulgarian), and it's the liturgical language of the Russian Orthodox Church.

Merci.

P.S.--I sure am glad all you professionals don't charge for all the education you dispense here! But you do have my gratitude.

I feared there would be no clear system, as the answer to the question took a while. From what you show here I would hesistate about choosing "ignious" . Or is it best to look at the most recent origin from L.igneus?

I will never learn all those by heart and so am condemned to keep
checking the books.

My dictionaries only contain the spelling 'igneous'
'ignious' is definitely not the dictionary spelling, but 'igneus' might be acceptable in America? The 'correct' English spelling is igneous. And don't worry, most native English spellers would have as much idea as you do how to spell igneous.

I don't think either ignious or igneus are anything but misspellings in USn English.

The reason for the 'e' would be that it is a part of the stem word. So you have 'aene' + 'ous', and the 'e' remains there. In acrogenous, the stem is just 'acrogen', so there's no other vowel.

From Etymonline.com:


I wonder who dropped e from wonders in the formation of wondrous. No one person decreed that it be dropped, I suppose. I don't know whether there is a term for adaptation of spelling to habitual pronunciation (someone here might), but I gather that the phenomenon is as old as writing.