1. The quality of being highly unpleasant
   "I flinched at the nastiness of his wound"
    
2. Malevolence by virtue of being malicious, spiteful or nasty
   "The nastiness in her remarks about her coworker's outfit was obvious to everyone";
   - cattiness, bitchiness [informal], spite, spitefulness
    
3. A state characterized by foul or disgusting dirt and refuse
   "The nastiness of the uncleaned public restrooms disgusted visitors";
   - filth, filthiness, foulness

See also: awful, nasty

Type of: malevolence, malevolency, malice, unpleasantness, unsanitariness

Antonym: niceness