Back up vs. backup

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The one-word backup works only as an adjective or a noun. When you need a verb, use the two-word phrasal verb back up. For example, when an American football team needs a player to back up their aging quarterback, they might trade for a good backup.


Below, backup is a noun in the first and third examples, and it’s an adjective in the second:

Stopping the vehicle, the deputy detected the odor of marijuana from inside and called for backup. [Ocala]

Backup lineman Lennie Friedman kept things interesting that day by going both ways at center and defensive tackle. [Chicago Tribune]

He is the backup who doesn’t back down on defense. []

And in these examples, back up functions as a verb:

Let’s back up for a second. [Seattle Post Intelligencer]

But according to the New York Times, investigators have yet to find any sanitation workers who can back up Halloran’s claims. [NY1]

What you need to do is back up the drive somewhere safe, then restore Windows before recovering your precious data. [BetaNews]