This is the 760th most frequent Japanese word.
まさに
Exactly; truly; just; right; precisely.
Here, 'まさに' is used to highlight the ideal or quintessential nature of the described scenery.
この景色はまさに絵に描いたような美しさだ。
This scenery is just like something out of a painting.
In this sentence, 'まさに' is used to stress the precise fit or truth of the subject being a genius.
彼はまさに天才だ。
He is truly a genius.
The word 'まさに' is used here to emphasize the correctness or exactness of the statement made by the subject.