noun

• (uncountable) The state of being in shadow or shade; (countable) a shadow.
  "If it be true, that there is a Firſt Being who has drawn or created all the reſt from nothing, man is truly his image; [...]. But an image, is but an image ſtill, and can be but an adumbration or ſhadow of the true perfect Being."
• (countable) A faint sketch; a brief representation, an outline.
  "There is another Difference of Sounds, which wee call Exteriour, and Interiour. [...] Wee ſhall therefore enumerate them, rather than preciſely diſtinguiſh them; Though (to make ſome Adumbration of that wee meane) the Interiour is rather an Impulſion or Contuſion of the Aire, than an Eliſion or Section of the ſame."
• (countable) A faint sketch; a brief representation, an outline.
  "ADUMBRATION, [in Heraldry] an abſolute taking avvay of the Charge or Thing born, ſo that nothing of it remains but the bare Proportion of the out Lines."
• (countable, uncountable, figuratively) A rough or symbolic representation; a vague indication of what is to come, a foreshadowing.
  "[W]here there is an obſcurity too deep for our Reaſon, 'tis good to ſit down with a deſcription, periphraſis, or adumbration; for by acquainting our reaſon how unable it is to diſplay the viſible and obvious effects of nature, it becomes more humble and ſubmiſſive unto the ſubtilties of faith: [...]"