Source: In common use
Gim (劍) is the name for the Chinese straightsword, from a large two-handed version to a standard size, up to shortswords and daggers.
The defining feature of the jiàn is not only that it's double-edged, but that both edges are exactly the same length. Therefore, a straight sword with a single long edge and double-edged tip section would still be considered a dāo, even if the tip section is completely symmetrical.
A good jian of the late Qing.
For more information, see the complete article: Jiàn (劍)