2. Adjective. Making a hissing sound ¹
3. Adjective. Childish or petulant (compare hissy fit) ¹
4. Noun. (American English) A tantrum, a fit ¹
¹ Source: wiktionary.com
Definition of Hissy
1. a tantrum [n HISSIES] / characterized by a hissing sound [adj HISSIER, HISSIEST] - See also: tantrum