a back gate / (figuratively) the anus, as a homophone for 肛門 and in contrast to 前門 (zenmon, “front gate”, figurative for vagina)

sluicegate, lock gate

speciality; specialty; subject of study; expert

a triumphal arch; in particular, the Arc de Triomphe in Paris

archaeology

education, study, learn / school / science

-ology; -ics; study of...

a male given name

inanimate/non-living/inorganic object/matter

a bioweapon, a biological weapon