@simrin - That's correct, the elective share law in the U.S. is based on jointure from English common law. I think to understand jointure and why our law on marital property is based on it, we have to understand the importance of property at that time.
Land was the most significant piece of property and it determined someone's class and power in society. Only men were allowed to own property though. Even though the legal system didn't allow women to own property, it guaranteed protection and financial support to women throughout their lives.
Also, when a woman got married, her father may have gifted property in her husband's name or she may have spent her money to buy property that her husband would own as well. So, even though technically the husband is the owner of land, essentially it's the woman's as well.
Men had to pay women dower as well. Sometimes instead of giving this money to women (which meant that you had to sell land for it and that was very valuable), husbands would make a deal with their wives. They would give their wives jointure- a piece of land- that was theirs for lifetime use, instead of paying a dower.
But since women couldn't own land officially, the land was actually held under a male relative's name. When both the woman and man died, the land would be passed on to their oldest son.
So jointure in both American and English history, is actually separate than dower. We have been using the term to mean only land, not money.