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.
knee jerk. You experience a knee jerk when your doctor taps your knee with a rubber mallet and your leg automatically kicks out. The idiom a knee jerk reaction means that you respond to something in an equally unthinking way. If you instinctively assume that someone who loves clowns wouldn't have much in common with you, that's a knee jerk, or automatic, reaction. This figurative meaning of knee jerk came from the physical reflex â which is called a patellar reflex by doctors, and which was discovered and named in the 1870's.