Owner
noun
The master is the owner who has dominance or control over something.
主 is usually used with other words to indicate a person who owns something or who is principally involved in an action. That might sound a little vague, so check out the collocations and context sentences to get a better grasp of this word!
The reading is of course different from what you learned with the kanji. Think of this:
The owner of those nude sheep (ぬし) doesn’t even need their wool, he just likes owning nude sheep. So he keeps them as pets and shaves them every day. He’s not interested in sheep with fur. Only nude sheep for this owner!
そのサイフの持ち主は私です。
I am the owner of that wallet.
落とし主は見つかりましたか？
Did you find the owner who’d lost it?
顔を見なくても、声の主はすぐ分かりました。
I recognized the owner of the voice easily, even without seeing his face.
この池には、古池の主と呼ばれる大きなトノサマガエルが住んでいます。
This pond is home to a large tree frog called the Lord of the Old Pond.