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Phrase(s): rear up
1. Lit. [for a horse] to lean back on its hind legs and raise its front legs, assuming a threatening posture or avoiding something on the ground such as a snake. (See also rear back.) • The horse reared up suddenly, throwing the rider onto the ground. • When the horse reared up, I almost fell off. 2. Fig. [for something, especially a problem] to raise up suddenly. • A new problem reared up and cost us a lot of time. • A lot of new costs reared up toward the end of the month.
McGrawhill's American Idioms And Phrasal Verbs