What is the name of the point when a spacecraft is furthest from the moon?

The extreme points of an orbit are generically called "apsis", and that's now the preferred term for all bodies. The furthest point in the orbit would be apoapsis, or for the Moon specifically, apolune, though as noted this term is now deprecated.

Note that this applies only to orbits. There is no Word for the furthest point of the entire journey.