Originally Posted By: TheFallibleFiend

JM: 'Words like missile and projectile are too broad'
They're too specific.

Well, yes, that too, it cuts both ways.

 Originally Posted By: TheFallibleFiend
JM: 'So a word that means, "A manipulandum that is the focus of, or central to, play in a game"'
Ah ... I misunderstood. I don't think manipulandum is something that is central to the play in a game. It's anything that one manipulates. I'm stumped.

Yes, manipulandum is also too broad. I've broached the subject with a number of people to no avail; my suspicion is that there is no such word. I guess I'll be off to commission a new work from my local neologist.