noun
mistress of the house; hostess; landlady; proprietress
Refers to a woman who is the head of a household, or who runs an inn, restaurant, or similar establishment. The specific English gloss depends on context.
旅館の女主人が玄関で迎えてくれた。
The landlady of the inn greeted us at the entrance.
彼女はこの家の女主人として、使用人たちをよくまとめている。
As the mistress of this house, she manages the servants well.
女将 is a more common and warmer term for a female proprietor of a traditional inn or restaurant, whereas 女主人 is more formal and can refer to any female head of a house.
Compound of 女 (おんな, 'woman') and 主人 (しゅじん, 'master, head of household'). The reading おんなしゅじん is a straightforward combination of the two words.