Englishfor English speakers
companion
Noun
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A companion is somebody who you spend time with, usually because you enjoy being with them.
In some places, it's best to travel with a companion.
Because she is blind, the dog is her constant companion.
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If mathx/math is a companion to mathy/math, mathx/math and mathy/math go together.
Pain is a natural companion to art.
Scientists noticed that this normal star circles an unseen companion.
virus
Noun
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A virus is a very small thing that can make people sick by getting into a living cell to copy itself.
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A computer virus is software that attacks your computer.