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A friend told me he had bought a new scabbard for his cell phone. I don't remember hearing that word for a good while and wonder why he didn't say holster, which I hear most often. Looked up both in four dictionaries and found none gave holster and scabbard as synonyms. Seems scabbard applies more to blades of various sorts, and holster is used for guns. As a kid, up to some age, we used the terms interchangeably. The lexicons saya scabbard is a sheath, and a holster is a case. Either can be used as noun or verb. Do you use or hear them used interchangeably?

I've never heard or even vaguely thought of holster and scabbard as synonyms. They are for guns and swords, respectively.

As to your friend's calling his cell phone case a scabbard, I have no clue where that one comes from.

As per Slava, holster and scabbard are not synonyms. In my experience and in what I can discover, scabbard is always a sheath for a sword or knife. Holster, whose ordinary definition is a sheath or case for a handgun, has a broader application to include a case for a cell phone, a slide rule (remember those), and any number of things, usually suspended from a belt.