Is there a single word for when two people have the same name? [duplicate]

Solution 1:

Could it have been cognominal? From the OED:

A. adj. 1. Having the same name or cognomen, like-named.
†B. n. One who or that which has the same name as another; a namesake. Obs. rare.
("cognominal, adj. and n." OED Online. Oxford University Press, March 2017.)

Only the noun is marked as obsolete/rare, but I'd venture to suggest that both forms are pretty darn unusual nowadays. However, I can imagine a word enthusiast using it in the context you describe.

Anna and my sister [Anna] may not have much in common, but they are cognominal!

At the less obscure end of the spectrum, the common term synonym is occasionally used for namesakes, since its root meaning is something like "similar name". This is the fourth (and last) definition of the word in the OED, but I would expect that usage today would generally be tongue-in-cheek.