一秒[ichibyou] one second
数秒[suubyou] several seconds
寸秒[sunbyou] a moment
秒針[byoushin] second hand (of clock)
秒速[byousoku] per second

秒読み[byouyomi] countdown
分秒[funbyou] moment
毎秒[maibyou] every second
秒時計[byoudokei] stop watch

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