The word "whicker" mainly refers to a sound made by a horse, which is a low whinnying sound that they produce when they become nervous or excited. Some synonyms for "whicker" include "neigh", "nickering", "winny", and "whinny". These words are also used to describe similar sounds made by horses, but they may differ in their pitch and tone depending on the situation. Other related words that can be used interchangeably with "whicker" are "snort", "huff", and "toss the head", which describe different ways in which horses communicate through sound and body language. Overall, these synonyms help convey the complex and nuanced ways in which horses communicate with each other and their human handlers.