The Collaborative International Dictionary of English v.0.48:

Tremie \Trem"ie\, n. [F. tr['e]mie hopper.] (Hydraulic Engin.)
   An apparatus for depositing and consolidating concrete under
   water, essentially a tube of wood or sheet metal with a
   hooperlike top. It is usually handled by a crane.
   [Webster 1913 Suppl.]