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 凸轮（把圆周运动转变为上下或前后运动的机械部件） (especially in compounds 尤用于构成复合词 a camera 计算机辅助制造；电脑辅助制造 a video/digital/traffic cam 视频/数字/交通摄像头 The police now have helmet cams—small video cameras attached to their headgear. 警察现在有了头盔摄像头-固定在其头饰上的小型摄像机。
Word Originlate 18th cent.: from Dutch kam ‘comb’, as in kamrad ‘cog wheel’.