a part on a wheel that sticks out and changes the circular movement of the wheel into up-and-down or backwards-and-forwards movement 凸輪（把圓周運動轉變爲上下或前後運動的機械部件） (especially in compounds 尤用於構成複合詞 a camera 計算機輔助制造；電腦輔助制造 a video/digital/traffic cam 視頻/數字/交通攝像頭 The police now have helmet cams—small video cameras attached to their headgear. 警察現在有頭盔攝像頭——附在頭盔上的小型攝像機。
Word Originlate 18th cent.: from Dutch kam ‘comb’, as in kamrad ‘cog wheel’.