虛線

dotted line / dashed line / (math.) imaginary line

emptiness / void / abstract theory or guiding principles / empty or unoccupied / diffident or timid / false / humble or modest / (of health) weak / virtual / in vain

thread / string / wire / line / CL:條|条[tiao2],股[gu3],根[gen1] / (after a number) tier (unofficial ranking of a Chinese city)