- chemicals whose molecular or ionic structure includes an unpaired ("free") electron, usually conferring high reactivity; in biological systems, most free radicals contain oxygen.
Definition from: CRISP Thesaurus via Unified Medical Language System at the National Library of Medicine
- Highly reactive molecules with an unsatisfied electron valence pair. Free radicals are produced in both normal and pathological processes. They are proven or suspected agents of tissue damage in a wide variety of circumstances including radiation, damage from environment chemicals, and aging. Natural and pharmacological prevention of free radical damage is being actively investigated.
Definition from: MeSH via Unified Medical Language System at the National Library of Medicine
See also Understanding Medical Terminology.