noun
reef; sunken rock
A rock or coral formation just below the water surface, hazardous to navigation.
船は暗礁に乗り上げてしまった。
The ship ran aground on a reef.
noun
hidden difficulty; pitfall
Figurative use for an unexpected obstacle or problem that lies hidden, often in plans or negotiations. Frequently appears in the phrase 暗礁に乗り上げる (to hit a snag).
See also: 暗礁に乗り上げる
交渉は暗礁に乗り上げた。
The negotiations hit a snag.