Definition of NASTY in the Definitions.net dictionary. Meaning of NASTY . What does NASTY mean ? Information and translations of NASTY in the most comprehensive dictionary definitions resource on the web. 7 meanings : 1. unpleasant, offensive, or repugnant 2. (of an experience, condition, etc) unpleasant, dangerous, or painful 3..... Click for more definitions. Nasty is an adjective used to describe something unpleasant, offensive, or harmful. Synonyms: Unpleasant, Mean , Harmful, etc. NASTY definition : 1. bad or very unpleasant: 2. unkind: 3. dangerous or violent: . Learn more.