do one good

do good

1. To have a positive effect on someone. In this usage, a noun or pronoun is used between "do" and "good." If you're feeling sad, getting out in the sunlight should do you good.
2. To focus one's energy on charitable acts. In this usage, "do good" is a set phrase. Monica has always been one to do good, so I'm not surprised to hear that she joined the Peace Corps.
See also: good
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

do one good

1. Be of benefit to one, as in I'm sure some fresh air will do her good. [Late 1400s]
2. Also, do one's heart good. Please, gratify, give satisfaction. For example, It does my heart good to see the young couple so happy.
See also: good, one
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.
See also: