Discussion Forum—A Way with Words, a fun radio show and podcast about language

In some languages they have not just singular and plural numbers, but also what's sometimes called "dual".   In the Bible, for example, we learn of a place called "Mahanaim", which means in Hebrew not "camps" but "[two] camps".   I gather that even in ancient Hebrew it wasn't used much, but I always found it interesting.

It got even more interesting once I realized that we have some dual forms in English, too.   We don't think of it much, but in addition to the plural pronoun "all", we have "both", which means "all two of them".   Likewise we have "either" (to go with "any") and "neither" (to go with "none").

So here's my question:   What other dual forms do we have?   I usually say I can think of four, but I can't remember the fourth one just now and I've always suspected there are more.   Anyone?