nail

nail in devotion or meditation, nails, as used for the crucifixion of Jesus, are taken as symbolizing the Passion.

Nails are the emblem of St Joseph of Arimathea, St Louis, and St William of Norwich.

Livy records the belief in ancient Rome that a plague could be checked by the dictator driving a nail into the Capitol.
nail in the coffin an action or event regarded as likely to have a detrimental or destructive effect on a situation, enterprise, or person.
nail jelly to the wall the type of an impossible task. The image was used by US President Theodore Roosevelt (1858–1919) at the time of the Panama Revolution in 1903, ‘You can no more make an agreement with those leaders of Colombia than you can nail currant jelly to the wall. And the failure…is not due to the nail. It's due to the currant jelly.’
nail one's colours to the mast refuse to admit defeat; declare openly which side one favours. The allusion is to a sea-battle in which the colours nailed to the mast cannot be lowered in defeat.
on the nail immediately, at once (usually referring to the payment of money). The explanations associating this phrase with certain pillars of the Exchange at Limerick or Bristol are too late to be of any authority in deciding the question.

See also bed of nails, when all you have is a hammer, everything looks like a nail, one nail drives out another, fight tooth and nail, for want of a nail.