- Something that introduces usually unexpected difficulties, problems, or changes.
Definition from: Metathesaurus Names via Unified Medical Language System at the National Library of Medicine
- A secondary disease or condition that develops in the course of a primary disease or condition and arises either as a result of it or from independent causes.
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
Related discussion in the Handbook
See also Understanding Medical Terminology.