adverb
certainly; without fail; by all means
Expresses strong desire or invitation; often used with ～たい, ～てください, or volitional forms.
ぜひ遊びに来てください。
Please do come and visit.
その映画はぜひ見たい。
I definitely want to see that movie.
noun
right and wrong; pros and cons
Formal noun; often used in discussions of morality or evaluation. Less common than the adverbial sense.
是非を論じる前に事実を確認しよう。
Let's check the facts before discussing right and wrong.
From Chinese 是非 (shìfēi), literally 'is and is not', used as an adverb in Japanese to mean 'by all means' and as a noun for 'right and wrong'.