What is the proper way to use Genius? Is he a genius? Is he genius? He is ingenius?
I am not.
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"Genius" is used as a noun in "He/she is a genius".
However, it is also used as an adjective these days: "That is a genius idea!"
"Ingenious" is an adjective too but "He is ingenious" does not mean the same as "He is a genius".