Is it ensure, insure, or assure?
Only a hint or suggestion of a much larger or more complex issue or problem: “The money missing from petty cash was only the tip of the iceberg of financial mismanagement.” This phrase alludes to the fact that the bulk of a floating iceberg is concealed beneath the water, leaving only a small portion, its tip, visible above.
A large piece of ice that has broken away from a glacier at the shore and floated out to sea.
Note: Most of the ice in an iceberg is underwater, leaving only the “tip of the iceberg” visible — a fact that is often alluded to in discussions of subjects in which the most important aspects are hidden from view.
An unemotional, chilly person; cold fish (1840+)