1
general::
Also, conspicuous by one's absence. Glaringly obvious by the fact of not being there. For example, One agenda item concerning publicity is conspicuous by its absence, or The bride's father was conspicuous by his absence. The idea is ancient; it was expressed by the Roman writer Tacitus, concerning the absence of Junia's brother and husband at her funeral procession. [Mid-1800s]
American Heritage Idioms