cusp and cusping

[Mark A. Mandel]

Jonathan says:
    >>>>>

OED lacks any reference to the recent widespread usage of the astrological
"cusp" in the general sense of "verge or initial stage," [...]

 <<<<<

Robert A. Heinlein's hit book "Stranger in a Strange Land" (1961) used
"cusp" frequently in the related sense 'critical moment, point at which a
decision must be made on which much depends'. One clue to the main
character's derivation of this metaphor is the expression "balancing on
(the) cusp", evidently alluding to the geometrical sense (OED Online):

[ad. L. cuspis, cuspid-em point.]
    4. Geom. A point at which two branches of a curve meet and stop, with a
common tangent; or at which the moving point describing the curve has its
motion exactly reversed. [...]

(Quoting from memory. The Heinlein, not the OED!)

-- Mark A. Mandel
[This text prepared with Dragon NaturallySpeaking.]

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