Changes in meaning of "bad" and "bad ass" [duplicate]

How did the definition of bad change over time? When did it change to mean good?

Solution 1:

Bad has been used to mean good since the 1800s.

The meaning of many, many words in English change over time. Many times they go back to a previous meaning. It's nothing new with the word bad. Another similar example is sick which since roughly the 80s in America has been used to also mean good or excellent.

If you really want to know why in particular bad has been used to mean good, a possible explanation is that many people see dangerous and reckless things as impressive. The thing I linked in the first sentence says how sick was used in skate culture to mean something good because risk and danger are considered good in that culture.