遺失[ishitsu] loss
遺失物[ishitsubutsu] lost article
一失[isshitsu] disadvantage (defect, error)
一得一失[ittokuisshitsu] gaining some and losing some
栄養失調[eiyoushicchou] malnutrition

過失[kashitsu] error
見失う[miushinau] to lose sight of
失う[ushinau] to lose
失する[shissuru] to lose
失せる[useru] to disappear

健忘[kenbou] forgetfulness
健忘症[kenboushou] amnesia
度忘[dowasure] lapse of memory
胴忘[douwasure] lapse of memory
年忘れ[toshiwasure] year-end drinking party

備忘[bibou] reminder
備忘録[bibouroku] notebook
忘る[wasuru] to lose something
忘れっぽい[wasureppoi] forgetful
忘れる[wasureru] to forget