The difference in height or depth between thevertex and therim of a curved surface, specifically used for optical elements such as a mirror or lens.
A place where the surface (of a seat, the earth, etc) sinks or droops, like a depression or a dip in a ridge.
1905, Louis Valentine Pirsson,Petrography and Geology of the Igneous Rocks of the Highwood ..., page43:
a mass of igneous rock[…] shown as a semicircular area of shonkinite exposed in the west wall of thesag. From the valley below, it appears as a dark cliff, perhaps 100 feet in height and a few hundred yards long.
2016 March 10, William T. Parry,Geology of Utah's Mountains, Peaks, and Plateaus: Including descriptions of cliffs, valleys, and climate history, FriesenPress,→ISBN:
Gunsight Peak north of thesag marks the southern end of the Malad Range that extends into Idaho. Complexly faulted Cambrian and Ordovician shelf sedimentary rocks are present[…]
sag (third-person singular simple presentsags,present participlesagging,simple past and past participlesagged)
Tosink, in the middle, by its weight or under appliedpressure, below a horizontal line or plane.
A line or cable supported by its endssags, even if it is tightly drawn.
The floor of a roomsags.
Her once firm bosom began tosag in her thirties.
(by extension) Tolean, give way, orsettle from a vertical position.
A building maysag one way or another.
The doorsags on its hinges.
1890, Great Britain. High Court of Justice. Probate, Divorce, and Admiralty Division,The Law Reports. Probate Division in the Courts of Probate and Divorce: In the Admiralty and Ecclesiastical Courts, and in the Privy Council, from Michaelmas Sittings, 1875, to 1890 (volume 5)
The weather became more and more threatening; the shipsagged to the leeward more than she ought.
