Do with a large amount of dried cilantro

Coriander, the plant, is the one whose leaves are called cilantro in many regions - the Spanish name for the plant. Of course, in some regions, the leaves are called coriander (or coriander leaves) as well. Coriander, the spice, is indeed the dried fruit/seeds of the plant, commonly sold both whole and ground. The seeds have a very different flavor from the leaves.

As for dried cilantro, the leaves? They're going to be pretty much flavorless compared to fresh cilantro. Cilantro loses its aroma quickly when heated or dried. Obviously there's still something left, or you wouldn't be able to buy dried cilantro, but it's not going to be a striking addition to a dish. If you can get it fresh, it's worth it.

Cilantro is one of the herbs that doesn't retain much flavor when it's dried; it's unlikely to be particularly tasty when made into a tisane. On the other hand, the dried seeds of the plant -- called "coriander (seeds)"* -- have a pleasantly tangy and floral/citrusy taste.

They are occasionally used as a flavoring agent in beer, so it's perfectly reasonable to think of them as a candidate for tisane. The flavor of coriander is not dissimilar to chammomile, and might complement that. It would probably make an interesting mix with black tea, too -- in fact, it should be noted that coriander is sometimes an ingredient in Masala Chai, the sweet Indian tea-milk-spice drink.

*In the US, the leaves are referred to as "cilantro", whereas "coriander" most often means the seeds (although sometimes the leaves).