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head (of a household); proprietor (of a store); proprietress; landlord; landlady
one's husband
(one's) employer; (one's) master
host; hostess
「主人」 has another reading with different meanings.
レストランの主人が自ら料理を運んできた。
The restaurant owner personally brought the food.
主人が仕事から帰ってきたら夕食にしよう。
Let's have dinner when my husband comes home from work.
犬は主人に忠実で離れようとしない。
The dog is loyal to its master and won't leave.