What's an intuitive derivation behind ODO's definition 1 that helps to remember its meaning?
1. adumbrate = [with object] Represent in outline:
Etymonline for adumbration: 1530s, from Latin adumbrationem (nominative adumbratio) "a sketch in shadow, sketch, outline," noun of action from past participle stem of adumbrare "to cast a shadow, overshadow, represent (a thing) in outline," from ad- "to" (see ad-) + umbrare "to cast in shadow," from PIE *andho- "blind, dark" (see umbrage).
My confusion arises from opposition between the clarity of an outline and haziness of a shadow. ODO's definitions 2 and 3 seem fitter, because they directly involve the idea of 'shadow'.