部門【ぶもん】
division (of a larger group), branch, field, class (subclass), group, category, department
専門【せんもん】
speciality, specialty, subject of study, expert, area of expertise
専門家【せんもんか】
specialist, expert, professional, authority, pundit
名門【めいもん】
noted family, noble family, prestigious school, organization, business, etc.
入門【にゅうもん】
becoming a pupil (of), becoming a disciple, entering an institution, beginning training, introduction (to), primer, guide, entering through a gate
宗門【しゅうもん】
(religious) denomination, sect
関門【かんもん】
barrier, checkpoint, gateway, hurdle, obstacle, trial
正門【せいもん】
main gate, main entrance
門扉【もんぴ】
door(s) of a gate
門下生【もんかせい】
pupil, disciple, follower
門松【かどまつ】
New Year's pine decoration
門外漢【もんがいかん】
outsider, layman, amateur