虽然两个单词都是提防、当心的意思.但LOOK OUT 有两个意思,还一个是向外看：This room looks out on a square.这间房间朝着一个广场.

LOOK OUT做“小心”时例句Look out!There's danger ahead!小心!前面有危险!Watch out 好像只有“密切注意”一个意思,且他一般与FOR连用,例句：Watch out for these pictures!(广告用语)注意这些影片上映时间!