nail; obstacle; undercover agent
Meanings
3 senses · 8 examplesnoun
nail (metal fastener)
neutralRefers to a common hardware item used in construction, woodworking, etc.
He hammered the nail into the wooden board.
There is a nail on the wall where you can hang a painting.
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This box of nails comes in three different sizes.
noun
hard nut to crack; stubborn problem; obstacle
informalA metaphorical usage describing a difficult person or situation that is hard to resolve.
That company is a hard nut to crack in these negotiations.
This historical issue has become a stubborn obstacle in the city's development.
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Persuading him to change his mind is a real tough one.
noun
undercover agent; mole; planted person
informalA metaphorical and colloquial term for a spy or informant placed within an organization.
The police planted an undercover agent in the criminal gang.
The company suspects a competitor planted a mole to steal trade secrets.