disremember (v.)

"forget, not remember," 1805, a colloquialism, from dis- "opposite of" + remember. Related: Disremembered; disremembering.

The improvements which are daily ushered to the world in our vernacular tongue afford reason to hope that it must soon arrive at the acme of perfection. With a great many of our wise folk, the old, absurd word forget is given over to oblivion, and the sonorous and elegant word dis-remember has completely taken its place. Ask one of these men any question to which he cannot return a ready answer, and he informs you that he dis-remembers. [The Port Folio, March 1810]