also: だいもん
noun
large front gate; main gate
Refers to a grand or imposing entrance gate, often of a temple, castle, or large estate.
寺の大門をくぐると、広い境内が広がっていた。
Passing through the temple's large gate, the spacious precincts spread out before us.
あの屋敷の大門はいつも閉まって
The main gate of that mansion is always closed.
Compound of 大 (large) and 門 (gate). The reading おおもん uses the native Japanese reading for 大, while だいもん uses the Sino-Japanese reading.