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

逸速く[ichihayaku] promptly
音速[onsoku] speed of sound
加速[kasoku] acceleration
加速運動[kasokuundou] accelerated motion
加速度[kasokudo] acceleration

快速[kaisoku] high speed
快速電車[kaisokudensha] high-speed train
角速度[kakusokudo] angular velocity
急速[kyuusoku] rapid (e.g. progress)
減速[gensoku] deceleration