Noah Webster's Dictionary (n.) Sand easily moved or readily yielding to pressure; especially, a deep mass of loose or moving sand mixed with water, sometimes found at the mouth of a river or along some coasts, and very dangerous, from the difficulty of extricating a person who begins sinking into it.

Multi-Version Concordance Quicksand (1 Occurrence) Acts 27:17 Which when they had taken up, they used helps, undergirding the ship; and, fearing lest they should fall into the quicksands, strake sail, and so were driven. (Root in KJV WEY WBS YLT)