1A gate — the structure forming an entrance in a wall, fence, or enclosure around a building, yard, or castle.
学校の門で友達を待ち合わせた。
I met my friend at the school gate.
城の大きな門がゆっくり開いた。
The castle's large gate slowly opened.
夜になると庭の門を閉める。
We close the garden gate at night.
門の前にタクシーが止まっている。
A taxi is stopped in front of the gate.
2A school or branch of learning centered on a single master or tradition, referring to the group of disciples that belongs to it. The phrase '〜の門を叩く' (knock at someone's gate) means to seek to become a pupil.
彼は有名な書道家の門を叩き、弟子入りした。
He knocked on the door of a famous calligrapher and became an apprentice.
その流派の門には多くの門下生がいる。
That school has many disciples.
3In biology, a 'phylum' — a major taxonomic rank below kingdom and above class (e.g. Chordata).
脊索動物門には人間も含まれる。
Humans are included in the phylum Chordata.
教科書では動物界の主な門ごとの特徴が説明されている。
The textbook explains the characteristics of each major phylum in the animal kingdom.
4A counter for cannons or guns, used to count the number of pieces of artillery (military context).
その戦艦には二十門の大砲が搭載されていた。
The battleship was equipped with twenty cannons.