Diot

Although “idiot” isn’t the first word that comes to my mind, unlike the other commenters, I still think this is quite ugly.

Not the pleasantest name out there.

Honestly, I hate this name for 2 reasons: One, it sounds like "diet", as in "Diet Coke". Second, if you add an "I" to the front, you get "idiot", apparently, and that would be horrible.

Just add the last name "coke" and this name is perfect.

Looks too similar to “idiot”.

I think it quite cute and very nice to type... I'm not too-too sure how it might be properly pronounced, but I pronounce it as "de-ot" personally and I think that has a nice tone. It makes a nice nickname or even a name.

Sounds like diet.

Ugly.

I just... No. This is asking your kid to get bullied in school.

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I recommend going with Dia (f) or Dio (m) if you want to maintain something similar. Maybe even Dot or Dottie, but that name might not age well with the child. Even if it's just a nickname it'll sound like you're either calling your kid Diet, or Idiot, both of which aren't preferable.

Add an 'i' before it. You get idiot.
Sorry, but this nickname would never be used in the modern English-speaking world. I'm not even sure if other countries would use this. Dionisia is a beautiful name. Too bad it has really bad (medieval) nicknames.