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regression
Webster Unabridged
Re*gres"sion (r?*gr?sh"?n), n. [L.
regressio: cf. F. régression.] The act of
passing back or returning; retrogression; retrogradation.Sir T. Browne.
Edge of regression (of a surface) (Geom.),
the line along which a surface turns back upon itself; -- called
also a cuspidal edge. -- Regression
point(Geom.), a cusp.
Webster Unabridged