" About Miss Debenham," he said rather awkwardly. "You can take it from me that she's all right. She's a pukka sahib.
"What," asked Dr. Constantine with interest, "does a pukka sahib mean?"

"It means," said Poirot, "that Miss Debenham's father and brothers were at the same kind of school as Colonel Arbuthnot was."
"Oh!" said Dr. Constantine, disappointed. "Then it has nothing to do with the crime at all."
"Exactly," said Poirot. "

― Agatha Christie , Murder on the Orient Express (Hercule Poirot, #9)