1. superlative form of great; largest in size, amount, extent, or intensity
2. most important, significant, or notable
3. most excellent or outstanding in quality or ability

Examples

• Mount Everest is the world’s greatest mountain peak.
• She showed the greatest kindness to everyone she met.
• This was his greatest achievement in sports.
• The greatest challenge was finding enough funding.
• Many consider him the greatest musician of all time.
• The greatest number of students chose pizza for lunch.
• Her greatest fear was speaking in public.