Every morning, for a month, on entering her office, she had been conscious, not of the room around her, but of the tunnels below, under the floors of the building-and she had worked, feeling as if some marginal part of her brain was computing figures, reading reports, making decisions in a rush of lifeless activity, while her living mind was inactive and still, frozen in contemplation, forbidden to move beyond the sentence: He’s down there.
There are no more uses of "marginal" in the book.
Show samples from other sources
It’s never this loud when the Commandant is in attendance, and I relax marginally, glad to avoid her.
Sabaa Tahir -- An Ember in the Ashes
It was marginally less awkward when the game started again, if only because there was so much to mock.
Laurie Halse Anderson -- The Impossible Knife of Memory