Why is "display-buffer-reuse-window" producing an error?

Version: GNU Emacs 29.4 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.43, cairo version 1.18.0)

I have an emacs configuration file which has followed me around through numerous different versions. And I have set the variable display-buffer-alist as follows:

(setq display-buffer-alist '(("*R Dired" (display-buffer-reuse-window display-buffer-at-bottom) (window-width . 0.5) (window-height . 0.25) (reusable-frames . nil)) ("*R" (display-buffer-reuse-window display-buffer-in-side-window) (side . left) (slot . -1) (window-width . 0.5) (reusable-frames . nil)) ("*Help" (display-buffer-reuse-widndow display-buffer-in-side-window) (side . right) (slot . 1) (window-width . 0.5) (reusable-frames . nil)))) 

But whenever I attempt now to determine the value of a variable (with C-h v variable-name), I get the error:

Symbol's function definition is void: display-buffer-reuse-window 

I'm not fully sure what's the problem here, or if I've misconfigured the display buffer as shown above. Maybe I've defined the display buffers wrongly - in which case, where do I look for the correct way of doing it? [I probably originally copied the definition from somewhere else, but that was too long ago...] Anyway, many thanks!