The oracle bone inscription of the character "眉" was comprised of "目" meaning "eye" and a long curve above, so this character is referred to the long curving thing above the eyes. It indicates the meaning of "眉" is eyebrow. Because the eyebrows and eyes are the most important parts in the face, "眉目" is usually referred to appearance. For example "眉目如画"means one's appearance is beautiful as if it is drawn in the picture. Then "眉目" extendedly means clue, for example "事情有了眉目".