The expression refers to using your senses to make determinations rather than depending on mechanical aides. You might hear someone say something to the effect, “I’m not certain what I’m doing, but it feels right.”

 According to Tony Kleu, pilots in early airplanes had no instruments to help them turn the plane and stay in control. They relied on their sense of balance and feelings transferred to their bodies by contact with the seat to determine the aggressiveness of the turn. A hard turn would cause them to slip in the seat. Thus “flying by the seat of your pants” is literal.

I never warmed to this phrase.  It means a youthful time, accompanied by carefree idealism, though recently in the U.S. it also means when someone is at the peak of their abilities.  People claim this makes sense because salads are fresh and wilt quickly.

Wikipedia says the phrase was coined by Shakespeare in 1606 in Antony and Cleopatra.  Cleo says “My salad days, / When I was green in judgment, cold in blood.”  There are many sites that agree: Shakespeare seems to make a reliable source.

The phrase became popular only from the middle of the 19th century and has had many literary uses.  Phrases.org notes that “Salad Days” was the title of a popular British musical in 1954.

It still leaves me cold.

NPR says the term filibuster “first appeared in the English language in 1591, according to the Oxford English Dictionary. The word was then `flee-booters’ [for ‘pirates’]. Its origins are probably Dutch, with some Spanish and French influences.” The pronunciation changed over time to our modern “filibuster”. In 1890 an obstructionist legislator was called a filibuster, and the word was on the road to our modern usage.

Online Etymology agrees with the origin of the word.

Free Republic offers more detail on the rise of our current usage.  In the early 1800s Senators began making long, irrelevant speeches on the Senate floor, which delayed or even stopped votes on legislation.  Battles over how to deal with the tactic ended in favor of the obstructionists, who were called filibusters by their opponents.  Today the old meaning is lost.  To filibuster is to disrupt and interfere with legislation through delay on the Senate floor.

I used a version of this expression in a book review I intend to post today, and decided I needed to learn the origin. It is commonly used when a person challenges that they want to discuss something they believe to be inaccurate or they want to challenge someone who they feel has wronged them. A posting on The Phrase Finder informs that the expression dates back to the sixteenth century and referred to a dog chewing endlessly on a large bone.

Last week there was a posting that described how purchasers of whiskey could determine whether it contained high or low alcohol content by giving it a hard, or “fair shake.” Higher alcohol content caused the froth or ‘head’ to disappear quickly. A test used to determine the “proof” of alcoholic beverages, a term that remains in use today, originated in the early 1700s. The beverage was “proved” by pouring some on gunpowder and lighting it. It was considered 100 proof or 57.15% alcohol by volume if it burned steadily with a blue flame. It was considered ‘under proof” if it failed to burn and ‘over proof’ if it burned too quickly.

Wiki Answers explains the current meaning is to give someone the chance to prove their honesty or reliability.  It originated to mean evaluation of the quality of whiskey. The U.S. government sought to pay off debt in the late 1700s by taxing whiskey distilleries. That caused many producers to make “bootleg” whiskey, and some had low alcohol content. You could determine whether alcohol content was high or low by capping some in a glass bottle and shaking it vigorously for a few seconds. The whiskey had low alcohol content if the top-layer of froth lingered. The “head” of froth disappeared almost immediately in whiskey with high alcohol content. The test had to be done with hard shaking, or a “fair shake.” The expression became a metaphor for business transactions and the measure of a personal character by the early 1800’s.