1. extremely small; visible only with a microscope
Usage: often replaced by ‘microscopic’ in modern usage
2. relating to or involving the use of a microscope
Usage: technical; often replaced by ‘microscopic’ in modern usage

Examples

• The microscopical organisms in the pond water were fascinating to observe.
• Scientists conducted a microscopical examination of the tissue sample.
• The microscopical details of the crystal structure revealed its composition.
• Even microscopical amounts of the substance could be detected.
• The microscopical analysis showed evidence of bacterial infection.
• Researchers used microscopical techniques to study cell division.