Hot answers tagged ortografia
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.
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.
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