Where do nicknames come from? I can understand William becoming Will, but why Bill? And Richard to Rich makes sense, but Dick? And for Pete’s (short for Peter’s) sake, why are people named John called Jack? That’s just stupid!
We did this one once before:
http://boards.straightdope.com/sdmb/showthread.php?threadid=7747
I now Jack.
It comes from French. “Jan” becomes “Jankin” - “-kin” being a diminutive - then “Jackin” then “Jack.” That’s how. Read it one of David Feldman’s books, either “Imponderables” or “Why Do Clocks Run Clockwise?” It has nothing to do with “Jacques” or “Jacquot,” which are the French “James.” Those derive from “Jacob,” James via the Greek, teh French versions from Hebrew.
As for Dick, I dunno.
Having read that earlier post, I didn’t see anyone directly finger my own WAG, so I’ll waste more perfectly good server space with it here.
You’re an young census taker, or tax recorder, or something, with two gifts that most folks in the Isles don’t have: literacy and the King’s English. Since you’re young and green, you’re naturally sent to the farthest corner of the Kingdom, somewhere where the folks speak in a brogue, or a burr, or something else that is almost incomprehensible to you.
You ask the name of the very first head of household you meet there what his name is, and he says, “I’m Rich Dringell.”
“What?” you ask.
“Rich Dringell, you stupid bloody bastard!”
So, you sigh to yourself and write down exactly what you heard:
“Dick Trickle.”
And he puts an “X” next to what you wrote down.
If you knew Richard, like I know Richard, you would call him a dick too. 
And how did you get Peggy from Margaret…same with Molly…
Or Sally from Sarah?
I know DAISY comes from Margaret, because that’s what the name means…I THINK…if I’m wrong, please, feel free to torture me.
Read the other posts - there is a link to when this was discussed before & that also links to the definitive Cecil answer…it is from Latin which means Pearl (& I knew that because it’s my middle name. Guess you don’t (normally) get nicknames for middle names though, as my nicknames are based on my first name & no one has ever called me Peg). Going back to meanings - with my first name I am called “fair pearl” (my mother must have been clairvoyant!).
Oh, & I’m getting the thumbscrews out now!
Fi.
Unfortunate name is Richard. Not only is he a dick but also a turd (Richard the third - cockney rhyming slang)
If Dick hadn’t been a nickname for Richard before
Nixon, it would have been after that Watergate
Dick Head.
What gets me is guys who prefer to be called Dick, like my father-in-law (whom it fits.)
WAG
Richard -> Rich -> Rick -> Dick
Name deevolution.
I’d like to echo don Jaime.
His French Connection seems convincing. The James to Jacob connection explains why after the ousting of the House of Stewart from the throne, the followers of the old King James were known as Jacobites.
I dunno Dick either, But it has been going on for a long time.
This couplet referring to the doomed King Richard the 3rd was written in 1485:
Intriguing.