Those allied powers were considerably astonished, when they arrived within a few minutes of each other, to find an unknown lady of portentous appearance, sitting before the fire, with her bonnet tied over her left arm, stopping her ears with jewellers’ cotton.
Quite alarmed at being the only recipient of this untimely visit, and the only spectator of this portentous behaviour, I exclaimed again, ’Pray tell me, Miss Mowcher, what is the matter! are you ill?’
’He’s a young man, sure?’ said the portentous waiter, fixing his eyes severely on me.
There are no more uses of "portentous" in the book.