The use of âholidayâ to mean âa missed spotâ appears to be that rarity in English etymology, a word or phrase that actually has a nautical origin. The original use of âholidayâ in the âmissed a spotâ sense, back in the 18th century, was in reference to crew members painting the decks of a ship or âpayingâ (sealing seams with tar or pitch) its hull.
The knee jerk reflex is when a tendon above the kneecap is tapped with a reflex hammer, which causes the whole leg to involuntarily jerk.
It's an expression/saying meaning: An immediate unthinking emotional reaction produced by an event or statement to which the reacting person is highly sensitive; It's origin is thus: From the tendency of the knee to jerk involuntarily when hit sharply, properly called the patellar reflex. That was recorded by Sir Michael Foster in his Text-book of physiology, 1877: Striking the tendon below the patella gives rise to a sudden extension of the leg, known as the knee-jerk..