a large floating mass of ice detached from a glacier
chiefly NAmer, informal an emotionally cold person
the tip of an/the iceberg
the small visible or known part of something much larger, esp something that is potentially troublesome, problematic, etc
prob a part translation of Danish or Norwegian isberg or Dutch ijsberg ice mountain. The phrase alludes to the structure of an iceberg, in which a small portion (generally reckoned to be a little over one tenth) appears above the waterline, belying the huge mass lying below it