The word is ra, which has layers upon layers of meaning.

You hear of yetzer ha-ra, the evil inclination, as being the root of things like sexual desire - but then again, the yetzer ha-ra is why God described the creation of humanity as "very" good (as opposed to the rest of creation, which was merely good).

ra is clearly an exceedingly negative term: it's hard to find a more negative term without getting really specific - for instance, an "abomination" (toievah is related to specific forbidden practices, such as bestiality).

Mostly, though, I'd describe it as the absolute opposite of tov, "good."

There is a chiasmus in the verse cited between light/dark and peace/evil - so that can either show the relative importance of peace, or perhaps show how evil is the opposite of peace (by "peace," I mean shalom, which is actually more accurately translated "wholeness," "perfection," "completeness," or the like)

The use of "ra" to mean "unlucky" as in ayin ha-ra (generally pronounced by those who would use the phrase ayin hora) is an Eastern European thing - it's closely associated with the folk religion there which was very concerned with evil spirits, &c.