the hebrew word for lioness is לביאה(le-vi-a) and for lionesses is לביאות (le-vi-ot)
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.
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