nicker

The word "nicker" most often refers to the low, soft, almost rumbling sound a horse makes. It is not a loud, sharp call like a neigh. Instead, it is usually a quiet sound of recognition, comfort, or affection. A horse may nicker when it sees a familiar person, when it greets another horse, or when a mare responds to her foal. The word is probably imitative in origin, shaped by the sound it describes. Although it is mainly used for horses, it can sometimes be used for similar soft sounds made by other equines, such as donkeys.

You will often see "nicker" in writing about animal behavior, especially when people describe the bond between horses and humans. A mare may nicker softly to calm her foal, and a horse may nicker when its owner comes near with food or simply returns after some time away. It is a small sound, but it can carry a clear sense of welcome, ease, and recognition.

The word also has a separate informal meaning in British English, where "nicker" means money, especially pounds sterling. People often use it in a loose way, as in "a few nicker," rather than to mean one exact pound. That money sense is slang and depends on context, while the animal sense is the clearer and more literal meaning. So the word can point either to a horse's soft greeting in a stable or, in British slang, to a bit of cash.