annual, biennial, half-yearly, monthly, quarterly, weekly, etc.
all-day, hour-long, two-hour, etc.
afternoon, breakfast, lunchtime, weekend, etc.
joint
The two companies held a joint meeting to discuss their new partnership plans.
general
The company called a general meeting to discuss the new safety rules with all employees.
bilateral, trilateral, tripartite
high-level, summit, top-level
exploratory, initial, introductory, preliminary, preparatory
crisis, emergency, urgent
crucial, decisive, key, vital
pre-inquiry, pre-session, pre-summit, etc.
post-election, post-results, etc.
board, cabinet, committee, council, departmental, family, ministerial, shareholders', staff, team, union
inter-governmental, inter-ministerial, inter-party, inter-tribal, etc.