Aunt
noun
Who is the chief mother? That's your aunt. And this aunt is the older sister of your mom or dad because she is the chief mother. An aunt who is a younger sister of your parent is 叔母, which is another word for "aunt" you already know!
The reading for this word is an exception. But you already learned the 叔母 which means aunt too. Well they have the same reading! So if you know one aunt, you know them all.
伯母はどうして私達の結婚式に来ようとしなかったんだろう。
I wonder why my aunt didn’t come to our wedding ceremony.