I understand what the phrase "letting on" means. It basically means to pretend, as in
He continued letting on that he had a lame leg.
It can also mean to disclose or reveal the true meaning of something.
Where did this term come from? When did it originate?
Best Answer
In "Glossary of supposed Americanisms" by Alfred Langdon Elwyn (1859), I find this:
The "Brockett" referred to appears to be "A Glossary of North Country Words", by John Trotter Brockett, FSA (1846) but I can't find the reference to "let on" or "laeta" in the samples that Google provides.
The first place I've found it used with the implication of "lying by omission", as in your example, is in a story called "Little Fairly" by Samuel Lover, Esq. R.H.A. in "The Dublin University magazine", Volume 1 (1833)