(law) any property that is considered by law or custom as inseparable from an inheritance is inherited with that inheritance
"The family lawyer confirmed that the antique ring was protected as a legal heirloom, ensuring it passed directly to my son along with the rest of the estate."
something that has been in a family for generations
"The antique pocket watch she inherited was an heirloom that had belonged to her great-grandfather before passing down through three more generations."
A valued possession that has been passed down through the generations.
"My grandmother's emerald ring is a cherished heirloom that she handed down to me on my wedding day."