Culée (buttress ©)

The massive transverse wall, away from the longitudinal wall of the church, which transfers the horizontal forces from the top part of the construction to the foundation.
Since the function of this part of an arc-boutant (flying buttress) is more or less identical to that of a contrefort (buttress) I have chosen to use the same translation.
The culée attached to the first flying buttress in the picture is that of the (Gothic) Notre-Dame in Cluny.
See also pile (synonym).

Notre-Dame - Cluny