So, the text of find familiar reads:
You gain the service of a familiar, a spirit that takes an animal form you choose.
The key word here is "spirit". One of my players, for example, is a warlock, and semi-for-flavor has a fragment of a forgotten god carried along with her. It's a long story, but the point is, she thinks the "spirit" that her familiar is, is a piece of the "forgotten god".
She subsequently thinks about the text on the spell that says:
As an action, you can temporarily dismiss your familiar. It disappears into a pocket dimension where it awaits your summons. Alternatively, you can dismiss it forever.
She wonders if she can, by banishing the familiar, send the familiar and whatever it's holding (e.g. a powerful magic object) back to the place it came from - in this case, the forgotten god, for him to feed off of.
My question is: is there an exact definition or ruling for this "spirit"? I thought it was like a will-o-wisp, or like a lost animal's soul, or something. Could she actually make this spirit a fragment of a larger being's spirit? Or is that more up to the DM's judgement? Honestly, I'm the DM, and I'm confounded by this.