This is a very good question, and while the term 'mortuary' sword has been is general use since the Victorian era, when it was coined, I'm not sure if anyone can exact the first date of its use or who was responsible.
Looking through old entries in catalogs and early writings might help secure its use in period but various sources would differ. I'm not sure if anyone has done primary research on this, but not aware of anything but continued use in works by many authors.
Ewart Oakeshott notes the Victorian romanticism which likely brought this term into use, and its misperception to having the death mask of Charles I , who was excecuted in 1649. As hilts with these types of faces existed much earlier this is of course incorrect. It is generally held that these hilts were in use as early as 1631 and fell out of general use by 1670.
The development seems to derive from the English 'cavalier' hilt, an evolution from dish guard thrusting swords and possibly earlier walloon type hilts with loop guards and secondary knuckle guards.
The association with Charles I may derive from a cavalier hilt with decoration with him and his queen Henrietta Marie which dates from c. 1630s.
These collectors terms, most of which seem to derive from the Victorian period, have become so firmly entrenched in the literature that they continue being used for expedience in discussion as so well known semantically.
|