Many common words come from nicknames. What would the words look like if the real name was used instead?
Well, instead of tomboy, tomcat, tommyrot, you would have Thomasboy, Thomascat, and Thomasrot.
Instead of magpie you would have Margaretpie; instead of nanny goat, Ann goat; instead of paddy wagon, Patrick wagon; instead of chuck wagon, Charles wagon.
Jack would be John. You would have blackjohn, Johnknife, Union John, John-of-all-trades, hijohn, and skyjohn.
A brown betty would be a brown Elizabeth. A teddy bear would be a Theodore or Edward bear.