nail

• nail [countable]
• 1 a thin pointed piece of metal with a flat top, which you hit into a surface with a hammer, for example to join things together or to hang something on:
• The key was hanging on a nail by the door.
• hammer/bang/hit a nail into something
• She hammered a nail into the wall.
• 2 your nails are the hard smooth layers on the ends of your fingers and toes:
• I've broken my nail.
• Stop biting your nails!
• She sat painting her nails (=putting a coloured substance on them).
• He still had dirt under his nails.
• ➔ fingernail, toenail
• 3

   nail in somebody's/something's coffin

  one of several bad things which help to destroy someone's success or hopes:
• Observers fear that this strike will be another nail in the coffin of the industry.
• the final nail in his coffin
• 4

   as hard/tough as nails

  very tough and not easily frightened, or not caring about the effects of your actions on other people
• 5

   on the nail

• a) British English if you pay money on the nail, you pay it immediately
• b) especially American English completely correct:
• They got it absolutely on the nail.

• ➔ hit the nail on the head

   at hit1 (26)

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.