Dictionary.net

• A strong steamboat used to break a channel through a frozen river, lake, etc.; a boat mounted on runners and propelled by sails on a frozen surface.

1919 - The Winston Simplified Dictionary
By William Dodge Lewis, Edgar Arthur Singer

• A strong boat, commonly propelled by steam, used to break a passage through ice; a boat to pass on ice.

1914 - Nuttall's Standard dictionary of the English language
By Nuttall, P.Austin.