Lewis & Short

immĕmŏrābĭlis (inm-), e, adj. [in-memorabilis] (ante-class.).

  1. I. Pass., unmentionable, indescribable = ἀδιήγητος: spurcidioi versus immemorabiles, i. e. unworthy to be mentioned, Plaut. Capt. prol. 56: spatium, Lucr. 6, 488.
  2. * II. Act., that will not tell any thing, speechless, silent: anus, Plaut. Cist. 2, 2, 3.