How to properly write “deplano”?

Question

There's a popular (and probably exclusively) guatemalan expression: deplano or de plano; meaning probably or surely, analogue to seguramente.

Example (provided for completion purposes):

-¿Dónde está Juan?
-Deplano se fue a comer.

Now, this might be a too colloquial or informal word to have its own official spelling, but I still wonder if there is a "proper" way to write it. My gut tells me it should be written as a single word, but it's easy to get orthography wrong.

Also, if you know of other places where it's said, please comment!

Answer 1

It's an adverbial phrase written as two words. It's somewhat recognized in the DRAE, via the judicial sense of de plano meaning "Que se adopta inmediatamente y sin trámites" (plano. de plano. 3.) which was likely picked up and used more colloquially, converting it from an adjective phrase to an adverbial along the way.

Answer 2

As @David explains in his comment it is written de plano.It is not written as a single word.

It means directly, going straight to the point.