1. a colorless, odorless gas that makes up about 21% of the atmosphere and is essential for most life forms to breathe
Usage: chemistry; biology
2. the chemical element with the symbol O and atomic number 8
Usage: chemistry

Examples

• Plants produce oxygen during photosynthesis.
• The patient was given oxygen to help with breathing.
• Oxygen is necessary for combustion to occur.
• Fish extract oxygen from water through their gills.
• The oxygen tank was nearly empty.
• Without oxygen, most living things would die within minutes.
• The atmosphere contains approximately 21% oxygen.