matertera

In medieval Spain matertera = maternal aunt

Peter Stewart...

This was well understood everywhere as the primary meaning, but the word
itself was occasionally found too useful for confinement to just one
relationship.

"Matertera" is indirectly (by way of an obsolete term, "matera itera") a
contraction of "mater altera", another mother, and in classical usage could
mean a mother-in-law as well as a maternal aunt.

The proper meaning for medieval clerics was defined - along with a
comprehensive array of precise relationship terms - by the second Council of
Douzy in 874, following Isidore of Seville (maybe better observed in Spain
than elsewhere), as follows:

"Sciendum est etiam, quia propinqui filii vel filiae ex parte patris agnati
vocantur, ex parte autem matris cognati appellantur; et partis frater vel
soror, patruus et amita...Frater matris, avunculus dicitur, soror matris,
matertera" (It is further understood that relatives of the son and daughter
on the father's side are called agnates, on the mother's side cognates; and
the father's brother or sister "patruus" and "amita"...the mother's brother
is called "avunculus", the mother's sister "matertera").

That didn't stop scribes from using the word loosely - as some people today
talk vaguely about "aunts" who might actually be cousins, or unrelated
family friends.

Context _always_ matters in translating Latin, not least from medieval texts
where this was a second language for the writer.

Peter Stewart