1. Concave on both sides
   - biconcave

See also: concave

• spirula
• Spirula peronii
• Spirulidae
• spirulina
• spiry
• spit
• spit and polish
• spit curl
• spit out
• spit up
• spital
• spitball
• spitchcock
• spite
• spiteful
• spitefully
• spitefulness
• spitfire
• Spitsbergen
• spitter
• spitting
• spitting cobra
• spitting image
• spitting snake
• spittle