Definition of "adumbrate"

From track level, its operating floor looks particularly capacious, but there is a vacant space at one end which was designed to accommodate the control panel for the Perth-Inverness C.T.C. scheme; this was adumbrated as long ago as the 1955 Modernisation Plan, but now seems to be regarded as an unjustifiable luxury.

1962 October, G. Freeman Allen, “The New Look in Scotland's Northern Division—II”, in Modern Railways, page 270

This piece will perform a micro-excavation of these toplayers of the literary soil to suggest anxiogenic literature has the potential not only to adumbrate the post-apocalypse, a common theme in contemporary literature, but also to anticipate the post-Anthropocene.

2020, Kristen Figgins, “The Integrity of Nature”, in Jonathan Elmore, editor, Fiction and the Sixth Mass Extinction, Rowman & Littlefield

Accordingly, even though readers always and understandably speak of the theories adumbrated by Socrates here as "Plato's theories", one ought not to speak of them so without some compunction--the writing itself, and also Plato the author, present these always in a spirit of open-ended exploration, and sometimes there are contextual clues indicating that Socrates exaggerates or goes what the argument truly justifies, and so on.

1996, John M. Cooper, “Introduction”, in Plato: Complete Works, Hackett, page xxii