cash cow

cash cow idiom
A dependable source of profit, as in The small-appliance division is this company's cash cow. Although this precise term dates only from about 1970, milch cow was used in exactly the same way from 1601.

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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