ice found attached to the bottom of an otherwise unfrozen stream or lake, often covering stones, etc.
anchor ice in American English
noun
ice formed below the surface of a body of water that attaches either to a submerged object or to the bottom
Also called: bottom ice, ground ice
Word origin
[1805–15, Amer.]This word is first recorded in the period 1805–15. Other words that entered Englishat around the same time include: backlash, diminishing returns, napoleon, polarization, soufflé