Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ob-littĕrātĭo (oblīt-), ōnis, f. [oblittero], a blotting out, erasing, effacing, obliteration; and, in partic., a blotting out from the memory, a forgetting, forgetfulness (postAug.): aeris oblitteratio, Plin. 34, 7, 18, § 47: vetustatis, Arn. 6, 194: praeteritorum, Amm. 30, 6, 1.