Both Uses of

omit
in
The Phantom of the Opera

And I should be ungrateful indeed if I omitted, while standing on the threshold of this dreadful and veracious story, to thank the present management the Opera, which has so kindly assisted me in all my inquiries, and M. Messager in particular, together with M. Gabion, the acting-manager, and that most amiable of men, the architect intrusted with the preservation of the building, who did not hesitate to lend me the works of Charles Garnier, although he was almost sure that I would never return them to him.†
Chpt Prol. *

R. "It was the one thought that did occur to me, monsieur, so much so that I omitted to follow Mlle.†
Chpt 5

Definition:

to exclude or neglect something