Great fun,lots of red herrings, but neat solutions!

Mind blown.

seemingly endless possibilities of connections - fiendish indeed!

I don't see why, for instance, "letter" and "pepper" couldn't exchange places; they both work in each other's categories. Same with "rose" and "wine". Or "whale" and "collar".

But,Wolfdog,isn't that the point of the game?

No, the point of the game is to have a grid that can be reasoned out logically; there should be only one way to separate the clues into four groups. Otherwise, it's a guessing game. Cross-over clues which *look* as if they could belong in more group make the puzzle more interesting, but there has to be an underlying reason why they go in one group and not the other.

I get what you're saying Wolfdog, but not sure I completely agree... you're right that having the groups be completely distinct would make for a great grid, but I don't think it is a necessity for a grid to be fun still.

For an example where crossovers are done well, have a look at #1396 (puzzgrid.com/grid/1396). At first glance, "full" looks like it could go with the other phases of the moon, and "queen" and "king" look like they could go with the other chess pieces. But if you try to go either of those routes, you'll find that you can't complete four groups, so it's possible to back up and figure out where they really belong.

4 x Related Prefixes.

Fully agree with Wolfdog below. No clues should be interchangeable between sets. This is one of the criteria set down in the original episodes of the TV show, and should be followed.
Swapping of pairs should stop at least 1 group being correct.