riderless
Adjective
Meaning
Having no rider; as, a riderless horse.
Source: Webster's dictionarySynonyms
Examples
The riderless horse, flanked by two Lance Corporals of the police Mounted Branch, stood just the east of the tent; further in the northeastern corner of the compound was the statue of the father of trade unionism in Guyana, Hubert Nathaniel Critchlow.
The riderless horse approaches the memorial.
The riderless horse is the Camp Verde Cavalry honoring one of its own who is no longer with it.