The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.

tholos


SYLLABICATION:
tho·los
PRONUNCIATION:
thls, -ls
NOUN:
Inflected forms: pl. tho·loi (-loi)
A beehive-shaped stone tomb of Mycenaean Greece, roofed by corbeling and
usually built into the side of a hill.
ETYMOLOGY:
Greek, round building with a conical roof.
(corbelling in this case means making roof of successively smaller
overhanging circles until a capstone can be applied.)

As a bit of trivia, "thole pins" preceded oar locks. A pair of sturdy pins
set into gunwale of skiff served as fulcra for oar to make rowing possible.