How about "lionesses"?
the hebrew word for lioness is לביאה(le-vi-a) and for lionesses is לביאות (le-vi-ot)
Looks like a borrowing from Latin!
Not likely, that is an ancient word that appears a lot in the Bible.
For example Bereashit 49:9 (Genesis 49:9)
Oh, thank you! Don't know there's a different word for that.
why is a feminine plural noun (male lions -- and I'm surprised that this is apparently feminine when plural) described with a masculine plural adjective?
(If I understood what you meant:) It is one of the cases that the plural of a male noun ends with -ות
Must be an irregular plural for male lions, because I wrote "the female lions are pretty" and it was wrong.
Yes, it is. some nouns have an irregular plural as the other gender, but "אריות" are still male lions.
Could it also be the pretty lions?
No, that'd be האריות היפים.
Lions are not "pretty". They may be beautiful, or handsome or majestic.
I'm not sure why the system rejected "nice" and "lovely" - since it accepted "nice" and "good" as translations for יפה previously
How would you say in hebrew the beautiful lions?
Someone else can explain why better than I can.
We said those hebrew words and got it wrong.