Xanathar's Guide to Everything introduces the ceremony spell. One of the options is to perform a wedding for 2 or more creatures:
Wedding: You touch adult humanoids willing to be bonded together in marriage. For the next 7 days, each target gains a +2 bonus to AC while they are within 30 feet of each other. A creature can benefit from this rite again only if widowed.
How is the term "widowed" defined for the purposes of this spell?
For reference, the Merriam-Webster definition suggests this refers to individuals whose spouse has died. However, when dealing with a world where creatures can return from the dead, and marriage can be a magical (rather than legal) concept, this may have some odd ramifications.
I can imagine some peculiar loopholes, which would lead to questions like:
If the marriage is polygamous, and only one spouse dies, do all of the other spouses count as being widowed?
Is there a maximum number of times a creature can qualify as being widowed? Or can they go Henry VIII-style if their spouses keep dying and they repeatedly get remarried?
If a spouse dies, and later comes back to life, are the other spouses still considered widowed?