rub up on

rub up on idiom
Refresh one's knowledge, as in I must rub up on my French before we leave for Paris. [Second half of 1700s] Also see brush up, def. 2.

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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