What does 凄い mean in Japanese?

terrible, dreadful, amazing (e.g. of strength), great (e.g. of skills), wonderful, terrific

凄い (Sugoi) — terrible · Japanese Dictionary

すごい

Sugoi

Usually written in kana.

Also read: スゴイ、すごーい、すご〜い、すっごーい、スゴい、スゴーイ

凄い (Sugoi) is a Japanese i-adjective meaning “terrible, dreadful, amazing (e.g. of strength), great (e.g. of skills)”.

i-adjectiveterrible; dreadful
i-adjectiveamazing (e.g. of strength); great (e.g. of skills); wonderful; terrific
i-adjectiveto a great extent; vast (in numbers)
adverbawfully; very; immensely

Sentences from Tatoeba (CC BY 2.0 FR).