To susurrate is to rustle or make a soft, whispery sound. There's nothing more relaxing than sitting outside on a summer night listening to the leaves susurrate overhead.
This verb is almost always used in a literary context, so you're most likely to find it in a poem describing the way a field of tall grass susurrates on a breezy spring day. You can also use it to mean a breathy whisper, like when the librarian susurrates, "Shh! You're in the library!" Susurrate comes from the Latin susurrus, "a murmur or whisper," which stems from an imitative root meaning "to buzz or whisper."