Definition of "aitch"

The word length, which contains only four sounds l e ng th, is usually spell'd thus, el ee en gee tee aitch.

1773 October, The Monthly Review Or Literary Journal Enlarged

"If you've got any drawing-room manners, or a dislike to eating peas with a knife or dropping aitches, you'd better chuck 'em away. They ain't no further use."

1898, H.G. Wells, The War of the Worlds, London: William Heinemann, page 257

She frowned, hearing Lim Cheng Po's voice, so English, so refined, so very English upper-class. And often she had had to tell Joe about his aitches.

1959, Anthony Burgess, Beds in the East (The Malayan Trilogy), published 1972, page 469