(archaic, possibly obsolete) fortress, redoubt / (archaic, possibly obsolete) important point, key

cause of an incident, usually a crime / ringleader, culprit, perpetrator

main building of central ministry

investigate, examine, inspect, inquire, inquire, survey

chief of any place whose name ends in 所, such as an office or research facility

(gynaecology) menarche; first menstruation

警察署長: head of a police station, superintendent

Numbers

short, brief

fault, weak point / (music) minor