world of good, a - Phrases/Idioms
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.
A great benefit, as in A vacation will do you a world of good. This expression uses world in the sense of “a great deal,” a usage dating from the 1400s. [Late 1800s]