Why is Bill short for William?
The question sounds like a setup for a joke: there is no B anywhere in William. The answer is a habit English has kept for roughly 700 years, and once you can see it, it turns out to be hiding inside many familiar names.
The rhyme habit
Medieval England shortened William to Will the ordinary way, by trimming. Then it did the playful thing: it rhymed. Will slid to Bill, and Bill stuck. That one small move, swap the first letter and keep the rhyme, is all over English naming.
The same swap gave Robert its Bob (from Rob), Richard its Dick (from Rick), Margaret its Peggy (from Meg), and Mary its Polly (from Molly). Bob, Dick, Peggy, and Polly all suddenly make sense together.
The one everyone gets wrong
Jack began as John, not Jacob. The natural guess is Jacob or James, and plenty of modern Jacks do answer to those names. But the nickname's origin is medieval John: England liked the affectionate suffix -kin, so John became Jankin, Jankin wore down to Jackin, and Jack was what remained.
The prettiest one
Daisy is short for Margaret. Margaret travels through French as Marguerite, which is also the French word for the daisy. So the flower name and Peggy are, underneath, the very same name.
The royal one
Harry is the medieval street version of Henry. For centuries, ordinary English simply said Harry where the records said Henry, and the current prince is living proof: he was christened Henry Charles Albert David.
One name, its whole family
Line up what the habit built and Margaret alone becomes Maggie, Meg, Margot, Greta, Peggy, Rita, and Daisy. Every one of them is Margaret. That is what nametree maps: plant a name and meet everyone it is quietly related to.
A reader question took this story one name further: How does Mary become Molly? The answer stacks a second medieval habit on top of this one.
Every pairing above is linked on its name page, with sources. When the scholarship hedges, we hedge.
Grow your family's name tree →