1A person who owns a house or apartment and rents it out for payment; the lessor in a rental agreement.
家賃を滞納したら、まず家主に相談したほうがいい。
If you fall behind on rent, you should talk to your landlord first.
アパートの家主が近くに住んでいるので何かあればすぐ頼れる。
The landlord of the apartment lives nearby, so I can rely on them right away if something happens.
家主に許可をもらって壁に棚を取り付けた。
I got permission from the landlord and installed a shelf on the wall.
2The owner of a house, or the head of a household responsible for managing home affairs.
この家の家主は先月引っ越してきたばかりだ。
The owner of this house only moved in last month.
家主として、家族の生活を支える責任がある。
As the head of the household, he has a responsibility to support his family's livelihood.