rid ‧ er /ˈraɪdə $ -ər/ BrE AmE noun [countable]
[ Word Family: noun : ↑ ride , ↑ rider , ↑ riding , ↑ override ; verb : ↑ ride , ↑ override ; adjective : ↑ overriding ]
1 . someone who rides a horse, bicycle etc ⇨ cyclist :
a horse and rider
2 . an extra or more detailed piece of information that is added to an official document and changes it slightly