the.com/tenderloin

means The tender, lean cut of meat from the loin area of an animal, along the backbone where muscles do the least work.

from From 'tender' + 'loin,' the word simply names what it is — the choice, soft part of the loin. The loin itself traces back through French to Latin 'lumbus' (the lower back/flank), the same root that gives us 'lumbar.' There's a separate, unrelated slang sense — a city's 'tenderloin' district, meaning a vice-ridden area — which the popular story says came from police officers who, with extra bribe money from the district's gambling and brothels, could finally afford the tender cut of meat instead of tougher stuff. It's a vivid tale, widely repeated, but treat it as folk etymology rather than settled fact.