flat out
adverb
Britannica Dictionary definition of FLAT OUT
informal
1
chiefly US
:
in a very clear and direct way
2
:
at the fastest possible speed
-
The car does 180 mph flat out.
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We've been working flat out. [=as hard as possible]
-
He was running flat out. [=as fast as possible]
3
US, informal
usually
flat-out
—
used to make a statement more forceful
-
This class is just flat-out confusing.
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The movie was flat-out lousy.
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She flat-out [=completely] missed the target.