凄い is one of い-adjective we use very frequently, most often in kana form. It is often translated as “extremely” and used in the adverb form, 凄く, such as 凄く大きい, or “extremely big.”
There are several theories of the origin of the word 凄い. The strongest theory is that 凄い was derived from an older word 過ぐ, which meant “super” or “extremely”. At that time, 凄い was used to express the sensation and feeling of being very cold - the kind of cold you’d feel in your bones , such as “biting cold”, or “spine chilling.” Over time, 凄い extended its current meaning from 過ぐ, likely because the two words sounded similar, and 過ぐ has fallen out of use.
Back then, 凄い was only used for negative things - however, in current Japanese, it can be used for either positive or negative meaning, although we tend to use it mostly in positive ways. For example, if we say 凄い人, that means a “great person” generally. When we want to express something as being “extremely bad”, we tend to use a different い-adjective 酷い, or “awful”, e.g. 酷い人 (=awful person).”
romysensei.com is super great!
Look, it’s raining extremely hard.