1. Not defended or capable of being defended
   - assailable, undefended, open

See also: vulnerable

• natural gas
• natural glass
• natural history
• natural immunity
• natural language
• natural language processing
• natural language processing application
• natural language processor
• natural law
• natural logarithm
• natural number
• natural object
• natural order
• natural phenomenon
• natural philosophy
• natural process
• natural resin
• natural resource
• natural resources
• natural rubber
• natural science
• natural scientist
• natural selection
• natural shape
• natural spring