Dick for Richard, Bob for Robert, Bill for William, and more
It originates from the 12–13th centuries (Middle English), in a time where a lot of people had the same names. Richard was also spelled Rickard, which obviously shortens to Rick (a nickname we still use today). From there, rhyming forms were created, getting us Dick. It also created Hick, which is a nickname that isn't in use today, but it's the origin of the word hick, in addition to last (family) names such as Hickson which are still in use.
The book Christian Names in Local and Family History expands further on this:
We can see immediately
how this might give rise to Roberts and Robertson and how the pet form would
lead to Robb(s) and Robson and the diminutives to Robbins, Robinson and
Robbie. Rhyming forms would produce Dobbs, Dobbin, Dobbinson, Hobbs,
Hobson, Hopkins and Hopkinson. Similarly the pet form 'Dodge' for Roger gave
rise directly to the surnames Dodge and Dodgson, Hodge and Hodgson, and the
diminutives produced Hodgett, Hodgkin and Hodgkinson. Such developments
were not confined to the common names nor indeed to male names, and the
process is one that is familiar to anybody working on early records. The purpose
here though is simply to remind those who are not familiar with such practices
what can lie behind latinised forms such as 'Robertus' and 'Ricardus'.
Peg for Margaret
This was created the same way (rhyming) as the other names in this group, but with more intermediary steps. From the Dictionary of Medieval Names from European Sources:
Margaret is the radiconym; take it and cut the name down to the first syllable, and you get Marg. In certain dialects, that r is going to be very lightly pronounced, giving us Mag. Magge (pronounced with two syllables) can be found in England as early as 1200, and not much later after that, you can find that hypocoristic form augmented with a diminutive suffix: Magota 1208 (this is a Latin form and would’ve been Magot in the vernacular). (We’ll give you three guesses as to why this name is no longer popular today….). By the end of the century, there are examples of the -a- shifting to -e-, e.g., Megge 1254, 1275, 1279, etc. You can also see it in Megota 1309 (also Latinized).
Jack for John
Even scholars don't agree on the exact origin!
It's likely one of these:
- From (Old) French Jacques
- From Jackin, a diminutive of Jan (itself a mere vowel away from John)
- From Picard-Flemish *Janke in the same way that Han became Hank(in), which became Hake. (The asterisk means it's a reconstructed form not recorded in written texts.)
Summarized from The Kinship of Jack: I, Pet-Forms of Middle English Personal Names with the Suffixes -kin, -ke, -man and -cot.
Jim for James
Middle English had James, Jame, and Gemme. From there it's a simple vowel change to get to Jim.