急度[kitto] surely
オリエント急行[orientokyuukou] Orient express
応急[oukyuu] emergency
応急攻撃[oukyuukougeki] hasty attack
応急渡河[oukyuutoka] hasty crossing

火急[kakyuu] emergency
緩急[kankyuu] pace
危急[kikyuu] emergency
危急存亡[kikyuusonbou] life-and-death matter

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