I recently discovered (not quite El Dorado) the ending -iant
Example:
Gogoniant
Llwyddiant
Diwylliant
These are “nouns” aren’t they? But is there a name for the group of them?
Reason I’m asking is that if I can workout the group I can guess at similar types of words. Diolch ymlaen llaw 
They’re abstract nouns, Anthony
Turns out knowing the collective name doesn’t help with the -iant pattern…worth a try!
I remember seeing “Cludiant Dros Nos” sign written on a truck some years ago, when overnight transport was a relatively new thing. So, I assume that Cludiant means (system of) transport.
Haulage according to the geiriadur academi 
Gwella - to improve: Gwelliant - improvement
Llwyddo - to succeed: Llwyddiant - success
Adlonni - to entertain : adloniant - entertainment
If you want a list of words, go to Geiriadur Prifysgol Cymru here: http://geiriadur.ac.uk/gpc/gpc.html, and put *iant in the search box. It will give you 1462 words to try in conversations and see whether anyone recognises them or not…
Amazing!!! Diolch Iestyn! I love it went you spot things like this.
-iant
-iad
-od
Ayyb
I love that. I’m hoping they don’t, to avoid my worrying about how to continue the conversation. So far I’ve only got as far as word 3 of 1462: Achosiant (causation). I’ll be thinking “because-ment”
wel, that’ll do to be going on on with then…
It worked! I heard the word gwelliant and knew they were talking about an improvement!
This is a great method for people that are going to have a go at writing an Englyn Milwr for the SSiW Online Eisteddfod this year. I’ll have to remember to suggest it!