| Idiom | Meaning | Example |
| flunk out |
fail a school program, fail a course
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If you flunk out of college, you will have to find a job.
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| fly-by-night |
bad, dishonest, not to be trusted
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He put his money in a fly-by-night company and lost it all.
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| fly by the seat of your... |
(See by the seat of your pants)
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| fly in the face of |
contradict, be opposite to
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These errors fly in the face of our reputation for accuracy.
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| fly in the ointment |
small problem, troublesome detail
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The fly in the ointment is that a boy saw you kissing Lola.
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| fly low |
drive a vehicle very fast, drive so fast you nearly fly
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On the freeway I was flying low - going over 200 km per hour.
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| fly off the handle |
become angry suddenly, lose your temper
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After Charlie flew off the handle he apologized for his temper.
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| fly on the wall |
(See a fly on the wall)
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| foggiest |
(See haven't the foggiest)
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| fold |
quit, stop operating
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The store folded during the recession - went bankrupt.
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