A mortise lock has one or two "tongues" that enter into the frame of the door to keep the door closed, one that is pushed by a spring and moved using the handle, and the other is moved by the key. Like for example the mortise lock in this image, featuring two "tongues":
https://commons.wikimedia.org/wiki/File:Einbausich-u-schl-3.jpg
I didn't know what other word to use, so I was using "tongue", but I notice that's not a complete alien word for such products, some vendors include the word "tongue", for example this one: Double Tongue Shift Door Lock Furniture Cabinet Door Drawer Lock