This phrase, then and now, suggests that someone is so gentle, or nonviolent, that they would not even harm a single, pesky little fly. It first appeared in 1778, read about it here .

There's no specific origin for this phrase. Read about the ideas behind it here . What it means when uttered is that a large number of people are falling sick and/or dead.

This one is pretty easy to figure out, it alludes to the uncontrolled way a loose axe-head flies off from its handle. It is first found in print in Thomas C. Haliburton's The Attaché; or, Sam Slick in England, 1843/4: "He flies right off the handle for nothing." Haliburton was an inventive writer and had a hand in the coining of several commonly used phrases: Ginger up Won't take no for an answer Today it means the same thing except in a figurative way - it means to lose control.

The original version of the succinct 'pigs might fly' was 'pigs fly with their tails forward', is first found in a list of proverbs in the 1616 edition of John Withals's English-Latin dictionary - A Shorte Dictionarie for Yonge Begynners: Pigs fly in the ayre with their tayles forward. There are other ideas about the expression, read about them all here .  The meaning of the expression is basically "that will never happen, no way no how."

There are two possible theories for this expression.  One of them centers around the stock market crash of 1929. In American English, from 1805 phrase fly a kite "raise money by issuing commercial paper on nonexistent funds;" According to The Toronto Star -- April 4, 1993, Sunday, FINAL EDITION: The phrase - loosely meaning go do something futile - originated during the stock market crash of 1929. It referred to "the useless bits of paper being tossed out the window" after the crash, she explains. The other theory is attested by 1942, American English, probably tracing to the popular song of the same name (lyrics by Johnny Burke), sung by Bing Crosby in "The Star Maker" (1939): Go fly a kite and tie your troubles to the tail  They'll be blown away by a merry gale,  Go fly a kite and toss your worries to the wind  And they won't come back, they'll be too chagrined. (for sources click here and here ) Today it basicall...