Something that is extremely difficult or nearly impossible to find because it is hidden among many similar things.
This phrase dates back to the 16th century, originally appearing as 'needle in a bottle of hay' in Thomas More's works around 1532. The imagery comes from the practical impossibility of finding a small, thin needle buried in a large pile of dried grass or hay, which would be both time-consuming and potentially dangerous.
The phrase has evolved with technology - before metal detectors, finding a needle in hay was truly hopeless, but now it's actually quite feasible! Interestingly, this idiom exists in many languages with similar imagery: French uses 'chercher une aiguille dans une botte de foin' and Spanish has 'buscar una aguja en un pajar.'
Complete word intelligence in one call. Free tier — 50 lookups/day.