tracery
trac.ery \'tra-s-(*-)re-\ n 1: architectural ornamental work with branching lines; esp : decora tive openwork in the head of a Gothic window 2: a decorative interlacing of lines suggestive of Gothic tracery
Webster's English Dictionarytrac.ery \'tra-s-(*-)re-\ n 1: architectural ornamental work with branching lines; esp : decora tive openwork in the head of a Gothic window 2: a decorative interlacing of lines suggestive of Gothic tracery