Taking a single operand, in math

• Having a single element
• Having only one component
• Having but one component
• Consisting of a single element
• Acting on a single number, mathematically
• Like certain math operations
• Molecules of only one kind
• Of one kind, in chemistry
• Having a single component

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1923, from Latin unus "one" (see one ) on model of binary , etc.