Eisteddfod is a compound word (second word soft mutates)
… the fod might be from “bod” but not the usual meaning “to be” … Bod is also an old Welsh word for a permanent residence etc…
Eisteddfod could also just mean a place of sitting…as someone is crowned and seated on a chair
Secondly … a Cae is a field … but maes can be an expanse of open land usually enclosed (and not a wooded tract of land!)… you see the name used sometimes for battlefields … also maes parcio - open area for cars parking!
Well, I think completely understanding the Eisteddfod takes quite some time to anyone not born and grown there! 
But maes…there’s also Maes Awyr, right?
Absolutely!
Caernarfon dialect question. Does “de” = di? As in: Efo dy card de.
Might have been a pun on S Wales debit card. It was said to me in jest.
I’m more familiar with it meaning “then” as in 'te. Like “da de?” - “good then?”
I always taken as a kind of “ini” in english (say it quickly). The same as “yndefe”, “ife”, and various others from elsewhere. An almost meaningless positive tag.
Yeah that kinda thing…
For “lock” my dictionary gives “clo”, “llifddor” and “cudyn”. Please, is “llifddor” the right word to use for a lock on a river? Thanks.
Sue
I’ve never heard it before but I would say yes. Llif is flood, flow or stream so I could see that working.
yes, llifddor is a lock-gate (literally “flow-door”), although for a canal lock in general (i.e. the whole thing) you can also use ‘loc’.
PS! clo is a lock in the sense of a door lock/gun lock/bolt
and cudyn is a lock of hair 
When I’m looking up a word to find out the Welsh for it, I generally check the word that I find in the other side of the dictionary to be sure of what sort of whatever-the-word-was it is. Especially when the dictionary in question doesn’t give that sort of hint in the first place.
For example, if I had looked up “lock” in the English to Welsh side, and gotten that list, I would then have looked each one up in the Welsh to English side to get the finer distinctions. It is very helpful!
Thank you very much, @siaronjames, @gruntius and @Sionned.
Since I mean the whole thing rather than just one gate, I had better go with “loc”.
Sue
There’s two things I’ve heard that I’m not sure of. They both seem to mean something like let’s go, here we go. they sound like this:
I think the first one is bant â ni - sort of like away with us, I suppose
Not sure of the second one sorry
…second one might be Cawn ni mynd…”lets go’…
Rich
Ha! Thanks @DanJones and @rich.
But now, I have to ask one one more:
Why Ma isie i ni feddwl amdani (meddwl mutated after ni)
and Cawn ni mynd (mynd does not)?
Yes you are right - it should mutate (according to the rules). I was aiming for the sounds that you had written down.
…where is it from (I don’t remember it from SSIW)…either the rules haven’t been followed or my guess may not have been correct 
Rich
It was right before a live song, when they say the title…blablabla…and then seemed to say this to get the band to start playing!
But it’s not the first time I hear native speakers ignore mutations, so this might be the case rather than your guess wrong, @rich !
It’s also used in this 1916 newspaper article - https://newspapers.library.wales/view/4015739/4015741
‘Coni mynd’ is almost certainly 'Co ni’n mynd - 'co is from acw there, but widely used in the S for here as well, like in 'co fe here/there it is.