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Phrase(s): rein something up
to bring something, usually a horse, to a stop. • She reined her horse up and stopped for a chat. • Rein up your horse and stop for a while., Phrase(s): rein up
[for a horse rider] to stop. • The equestrian reined up and dismounted. • We all reined up and waited for the cars to pass by.
McGrawhill's American Idioms And Phrasal Verbs