1. to convert (an atom or molecule) into an ion by removing or adding electrons
Usage: British spelling; American English uses 'ionize'; chemistry and physics term

Examples

• Ultraviolet radiation can ionise oxygen molecules in the upper atmosphere.
• The electric field ionises the gas, creating a plasma.
• When salt dissolves in water, it ionises into sodium and chloride ions.
• High-energy particles ionise atoms as they pass through matter.
• The process of ionisation releases free electrons and positive ions.