I WAS SEARCHING around for historical oddities the other day in Charles Downey's "Stabbed with a Wedge of Cheese . . . and other Cultural Oddities"(NY: Wm. Morrow, 1992).

Ever wonder where the expression "dead as a doornail" came from?Downey found that in 14th century England, a doornail was the plate upon which a door knocker was struck. The doornail was said to be dead because it had been struck so hard and so often that there could be no life left in it.

Another familiar one is "he is not worth his salt."

In Roman days, part of a person's pay was given in salt, at the time a valuable commodity. The Latin salarium ("the money given to the soldiers for salt") came to mean payment for services rendered. Today, the Latin salarium (from the Latin sal - salt) shows up in the English salary.

"Son of a gun" started when officers and sailors of seafaring nations took their women with them on long voyages. Births at sea were common. When a woman had a difficult delivery, she was taken out alongside the vessel's cannon. When she least expected it, the gun was fired, startling the woman and providing the necessary trigger to give birth.

"Getting down to brass tacks" comes from 19th century rural America.

A general store used to sell a little bit of everything, material included. Instead of getting a yardstick for every purchase, the merchants pushed brass tacks into their counters to mark yards. Then instead of guessing at the length of the material, they would put it "down to brass tacks."

Most of us are fond of saying, "I was just being devil's advocate."

In ancient Rome, when a candidate for sainthood was represented at the pope's court, the advocatus diaboli ("Devil's advocate") gave every possible argument against canonization. Speaking for sainthood was the advocatus dei (God's advocate).

When you say you intend to get the job done, "come hell or high water," the phrase refers to a ghastly execution reserved for 17th century pirates.

At Execution Dock in Wapping, England, pirates, like the notorious Captain Kidd in 1701, were hanged by their wrists in a pit at low tide and left exposed until three tides had submerged them.

Have you ever been told you could not "hold a candle" to someone else?

Among 15th century gamblers in England, stableboys or servants were paid a few pence to hold a candle behind the gambler during all-night games so he could see his cards. But when he lost all his money, other gamblers contemptuously remarked the man was no longer able to hold a candle.

Ever "steal" anyone's "thunder"?

English playwright John Dennis created a process of thunder to accompany his play, "Appius and Virginia" in 1703. Unfortunately, his work was not well-received, and it closed early.

A few nights later, Dennis saw a production of "Macbeth" and discovered his sound effects were being used in the scenes with the witches. He jumped up and cried out, "See how the rascals use me! They will not let my play run, yet they steal my thunder."

Finally, what about "Kick the bucket"?

The frame from which a freshly killed pig was hung in old England was known as a "bucket." If the pig thrashed about, it kicked the bucket. Also, during that time, a depressed person would commit suicide by standing on an upside-down pail with one end of a noose tightly fastened to his neck and the other tied to a beam.

His last act in the world was to "kick the bucket."