M-HH is certainly not wrong with her definition, but I think there is a nicety of meaning here that, although probably inapplicable in the present context, might be of general interest all the same.

'To do well by someone' doesn't JUST mean 'to treat them well' (directly) — it can also mean 'to act in such a way as to indirectly do them some good'

For example, you might well say: "X did well by his cousin in introducing him to that businesswoman, because she's now given him a job"

It should also be noted that this expression sometimes has a slightly old-fashioned ring about it these days.

it's not an idiom, it's just one of the meanings of this preposition 'by':

concerning; according to :
anything you do is all right by me
(you could also say: anything you do is all right AS FAR AS I AM CONCERNED.

she had done her duty by him.
(you could also say: she had done her duty AS FAR AS HE WAS CONCERNED or ACCORDING TO HIM)

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Note added at 5 hrs (2006-09-29 17:54:57 GMT)
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and how is it different, dusty? you didn't point out...

do you understand the difference between idiomatic usage:
using, containing, or denoting expressions that are natural to a native speaker
and
an idiom (an idiomatic expression):
a group of words established by usage as having a meaning not deducible from those of the individual words (e.g., rain cats and dogs, see the light)?

once one knows this particular meaning of the preposition 'by' explained by me, there shouldn't be a problem, really.

and my explanation is the only one so far that addresses the asker's question - the highlighted preposition 'by'.

i hope that you will not object to the fact that 'by us' here means 'as far as we are concerned'?



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Note added at 6 hrs (2006-09-29 18:32:16 GMT)
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i probably should have applied my explanation to YOUR sentence, which could also be put the following way with the same meaning:

... those who disregard or injure us really could have done better AS FAR AS WE ARE CONCERNED.

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Note added at 8 hrs (2006-09-29 20:29:22 GMT)
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from the following example you can see that there is nothing idiomatic about the expression 'to do better' (the meaning of which is clear) to which 'by sb' is added, and in every case 'by' can be substituted with 'as far ... this sb ... is concerned':

as far as ... we ourselves, women, our children ... are concerned

nor have i noticed any old-fashionedness about it - it's a recent article...

We’ve done well but we need to do more, we need to do better.
We need to do better by ourselves.
We need to do better by women.
And we need to do better by our children – our future
http://64.233.183.104/search?q=cache:sGZrwt5u29UJ:www.waitak...

i think this blog might help


letters from mr. mom
To: H
From: [email protected]
RE: no subject

H,

I miss you, kid. I miss a lot of things and wish I had done better by you guys.

Love you,

Dad

To: [email protected]
From: H
RE: WHAT?

Dad,

Done better by us? Are you kidding me??
I don't think I know anyone whose father was more involved in their childhood. Now, I know things are really hard on you right now, but you can't seriously think you were a let-down as a father. Who put their socks in the dryer so we could put them on after sledding, when our toes were the color of raspberries? Who took us all the way down to 7-11 in that little red wagon, with us making obnoxious noises over the gravel all the way... and didn't strangle us? Who taught me that boys are for carrying heavy things and paying for my movie? Yeah, you made us weed the garden and that sucked. Yeah, you ruined some stuff in the wash. And sometimes you yelled... But I yelled back. You think things would have been BETTER if you were the typical bread-winning father -- always in the office and never home? I hardly think so. I don't think you could have done better by us. So there.

Love,

H