Sorry if my question is a bit unclear, but I used to know this word, and now it totally escapes me.
Here's an example:
There are two potions that cause you to fall in love or to fall out of love. They ______ are the red potion and the blue potion.
The blank space is a specific word that connects the first word in the previoue list with the first word in the list after. And then the second word of the first list to the second word of the next one.