In the introduction to Audible version of Swords against Death by Fritz Leiber, Neil Gaiman states (about 1 minute into the "Opening Credits"):
The significance of the title of the book will become more apparent as the series goes on. Especially in the later books Ice Magic and The Knight and Knave of Swords you learn what the title of this book really means - Swords against Death.
Now, it has admittedly been a while since I read the Lankhmar series, but I can't say I ever divined any special meaning in the titles of the books, and upon hearing it now I also struggle to attribute any meaning to it.
Admittedly I didn't reread the books mentioned by Gaiman to see if that jogged my memory. However I did a fair bit of Googling and couldn't find any discussion or mention of what the significance of the book title might be.
Can someone here remember their Leiber better than me, and enlighten me on what the significance or meaning of the book title Swords against Death is?