gate, counter for cannons
門 centers on a physical gate or doorway: an entrance or opening that can be closed. The counter-for-cannons sense is a specialized historical usage treating cannons as gate-like objects.
門 is a pictograph of a double-leaf gate, with the two vertical halves representing the swinging doors. The modern form preserves this gate image clearly.
The two tall side strokes are the gateposts, and the inner horizontal strokes are the doors. Picture a grand entrance: 門 is a gate.
For モン, imagine a monk standing at the gate: monk -> モン, and the monk opens the gate.
speciality; specialty; special subject of study; area of expertise; (one's) field; (one's) major
division (of a larger group); branch; field; class (subclass); group; category; department
gate
becoming a pupil (of); becoming a disciple; entering an institution; beginning training
strait with a roaring tidal ebb and flow; whirlpool; maelstrom
distinguished family; famous family; noble family
(medical) specialist
main gate; main entrance
before the gate; in front of the gate
family; clan; kin
barrier; checkpoint; gateway
door
school gate
turning someone away (at the front door); refusing a visitor; shutting the door in someone's face; refusal of admission
gateway to success
back gate
one's pupil; one's student; one's follower
door(s) of a gate
New Year's pine decoration
pupil; disciple; follower
outsider; layman; amateur
Panmunjom (Korea); Panmunjeom; Joint Security Area (Korean Demilitarized Zone)
(religious) denomination; sect
vocational school; technical school