badness; poor quality; how bad something is
A noun expressing the bad or poor quality of something, often used with の or に to point to what is unsatisfactory.
mischief; naughty act; mean trick
Common in the pattern 悪さをする, meaning to do something naughty, mischievous, or deliberately troublesome. Often used for children, animals, or minor wrongdoing.
I was surprised at how bad the food tasted.
This hotel has a good location, but the poor service stands out.
I am having trouble with the poor signal.
The children got up to mischief in the garden and trampled the flowers.
While we were out, the cat got into mischief in the kitchen.
The child got scolded by the teacher for misbehaving.
The delinquents did something harmful to the neighbors.
良さ expresses the goodness or quality of something, the direct opposite of what 悪さ expresses about badness or poor quality.
悪さ is counted with 回 when talking about how many times an act of mischief was done, as in 一回悪さをした.
Formed from 悪い, 'bad,' with the nominalizing suffix さ, which makes a noun meaning 'badness'; the mischief sense is an extension of doing something bad or naughty.