throw a monkey wrench in(to) (something)

throw a monkey wrench in(to) (something)

To disrupt, foil, or cause problems to a plan, activity, or project. Primarily heard in US. We had everything in line for the party, but having the caterer cancel on us at the last minute really threw a monkey wrench into our plans! It'll really throw a monkey wrench in the works if the board decides not to increase our funding for this project.
See also: monkey, throw, wrench
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

throw a monkey wrench into

Sabotage or frustrate a project or plans, as in The boss threw a monkey wrench into our plans when he said we'd have to work Saturday. This transfer of industrial sabotage-that is, throwing a tool inside machinery-to other subjects dates from the early 1900s.
See also: monkey, throw, wrench
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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