Detrimentalness refers to the degree to which something is harmful, damaging, or negative. However, there are several synonyms that can be used to describe the same concept. For instance, the word "harmfulness" can be used to indicate the degree of danger posed by something. "Destructiveness" is also a synonym for detrimentalness and refers to the level of damage something can cause. "Detriment" can be used interchangeably to refer to something that causes harm or injury. "Negativity" can also convey the same idea as detrimentalness, which refers to the presence of critical or pessimistic attitudes. Overall, all of these synonyms convey the underlying idea of something having an adverse impact or being harmful in some way.