As a Noun: 1. A day taken off work with pay for genuine or, especially, feigned illness. Informal English = sickie. 2. The time that a person is officially allowed to spend away from work because of illness or injury. English = sick leave. As a Verb or Adjective: 1. To take a day off work with pay for genuine or, especially, feigned illness. Informal English = take a sickie, chuck a sickie. 2. To officially spend time away from work because of illness or injury. English = take sick leave, (be) on sick leave.