There are several synonyms for the word "nickerer". One of the most common is "neigher", which refers to a horse that makes a neighing sound. Another synonym is "whinnyer", which also refers to a horse that makes a high-pitched, whinnying sound. "Snorter" is another synonym that can be used to describe a horse that makes a snorting sound, which is often a sign of excitement or agitation. "Prancer" is another synonym that can be used to describe a horse that tends to prance or move around a lot, often in excitement or anticipation. Ultimately, there are many different terms that can be used to describe horses and their various sounds and behaviors.