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head (of a household, etc.); leader; master
owner; proprietor; proprietress
subject (of a rumour, etc.); doer (of a deed)
guardian spirit (e.g. long-resident beast, usu. with mystical powers); long-time resident (or employee, etc.)
husband
you
「主」 has other readings with different meanings.
池の主と呼ばれる大きな鯉が姿を現した。
A large carp called the master of the pond appeared.
この古い屋敷の主は百歳を超える老婦人だ。
The owner of this old mansion is an elderly woman over 100 years old.
彼がこの店の主です。
He is the owner of this shop.