• 門もん — gate
• 専門せんもん — specialty / field of study
• 名門めいもん — prestigious family / school
• 入門にゅうもん — introduction / getting started
• 門番もんばん — gatekeeper
• 門前もんぜん — in front of a gate (often of a temple)
• 部門ぶもん — department / division
• 門松かどまつ — New Year’s pine decoration (placed at the gate)
• 門戸もんこ — gateway / door (often metaphorical)

This kanji often appears in words related to buildings, entrances, and areas of knowledge. The shape looks like a gate, symbolizing boundaries and points of entry — whether physical or conceptual.

門もんを通とおって入はいります。
Go through the gate to enter.

この大学だいがくは 専門せんもん分野ぶんやの入門にゅうもん講座こうざが充実じゅうじつしています。
This university offers well-structured introductory courses in specialized fields.