tail-bay

from The Century Dictionary.

• noun In a canal-lock, the space between the tail-gates and the lower pond.
• noun In a framed floor, one of the spaces between a girder and the wall.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arch.) One of the joists which rest one end on the wall and the other on a girder; also, the space between a wall and the nearest girder of a floor. Cf. case-bay.
• noun The part of a canal lock below the lower gates.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun architecture One of the joists which rest one end on the wall and the other on a girder.
• noun architecture The space between a wall and the nearest girder of a floor.
• noun The part of a canal lock below the lower gates.