genuine

In the 1590s, English picked up genuine from Latin genuīnus, a word that first meant something like “native” or “innate” before it hardened into “real, not counterfeit.” Latin writers tied it to gignere, “to beget,” which puts genuine in the same family as gene, genus, generate, and progeny — all those birth-and-blood words. There’s a delicious rival story, though: some people thought it came from genu, “knee,” as if a Roman father officially claimed a baby by placing it on his knee. That’s probably folk etymology, but it is wonderfully physical — a word about authenticity with a literal kneecap in the background. So when you call something genuine, you’re really saying it has the right family line, not just a convincing costume.