Reason: There are some cases of both appearing together and I wondered if that was redundant.
Actually, I also hoped to figure out whether there should be some distinction between the coverings for short and long blades. AFAIK "scabbard" is standard for a sword, but is there a term reserved for daggers and knives?
BTW I took the liberty of creating a Wiki definition for "holster," pointing out that knives and daggers should use "sheath" or "scabbard" instead. If a janitor or mod approves of this, then a certain number of knife (or dagger) pics would have to be re-tagged...
Looking at Merriam-Webster's online dictionary, scabbard's definition is that it's a sheath for a sword, dagger, or bayonet. Honestly though, I've never heard it used for a dagger or a bayonet's sheath.
If it is deemed worthwhile to have a line between a sword's sheath and sheaths for other weapons, then it'd be best to have for swords scabbard and implicate it to sheath.
Funny, wikipedia defines that scabbard is the sheath for a sword or other large bladed weapon, or large gun. Yet, there is no wiki page for sheath. It just leads to a list which would lead you back to scabbard.