adj
imaginary
ih-MAD-zhih-nuh-ree
adj
1
Not real; existing only in the mind or imagination.
"As a child, she had an imaginary friend named Bibbles."
"The map showed an imaginary line dividing the two territories."
2
In mathematics, describing a number that is a multiple of the square root of -1.
"The equation had two imaginary roots."
How to Use Imaginary
Learner’s notesIn plain EnglishNot real, or made up — or, in math, a number involving the square root of a negative number.
Common mistake
Don't confuse with "imaginative," which describes creative thinking rather than something unreal.
Easily confused with
Common pairings
imaginary friend
imaginary number
imaginary line
Word Forms
more imaginary comparative, imaginaries plural, most imaginary superlative
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Fill the Gap
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As a child, she had an _____ friend named Bibbles.
Etymology
From Latin imaginarius, "relating to images or fancies." The mathematical sense was coined by René Descartes in 1637, who used it dismissively for numbers he thought couldn't really exist — the name stuck even after mathematicians accepted the concept.