- (also sprocket wheel)
a wheel with a row of teeth around the edge that connect with the holes of a bicycle chain or with holes in a film, etc. in order to turn it 链轮；输片齿轮 one of the teeth on such a wheel 链轮齿；链齿 
Word Originmid 16th cent. (denoting a triangular piece of timber used in a roof): of unknown origin.