the GNU version of the Collaborative International Dictionary of English
n. A pipe to let off water.
The Century Dictionary and Cyclopedia
n. A pipe laid at the level of the bottom of a canal for letting off the water.
Word Usage
"First, the water might be run off by a descending pipe, if an offlet could be got at the depth of thirty-five or thirty-six feet, and any air might be extracted by a small pump."