The word "Henchman" originally comes from an old word meaning…?

The "hench" in "henchman" comes from the Old English “hengest,” meaning "horse," often with particular reference to a stallion. It is found in English since 1360, and similar words are found in several other languages as “hingst” (Danish and Swedish), “hengst” (Dutch and German), or “hings” (Afrikaans). The word appears in the name of Hengest, the Saxon chieftain, and still survives in modern English in placenames and other names beginning with "Hingst-" or "Hinx-." The word “henchman” was often written “henxman” in mediaeval English.

Young henchmen rode or walked at the side of their master in processions and the like. They appeared in the English royal household from the 14th century until Queen Elizabeth I abolished the royal henchmen, also known as the children of honour.

The usage of the word to mean "groom" or "attendant" became obsolete in England from about the middle of the 17th century. However, it was retained in Scotland to signify the personal attendant of a Highland chief. In this sense the word was synonymous with "ghillie," the faithful personal follower of a chieftain, the man who stands at his master's side, ready for any emergency.

The modern sense of "obedient or unscrupulous follower" is first recorded 1839 and is often used to describe an out-and-out adherent or partisan, ready to do anything.