asymptote (n.)

"straight line continually approaching but never meeting a curve," 1650s, from Greek asymptotos "not falling together," from a- "not" (see a- (3)) + assimilated form of syn "with" (see syn-) + ptotos "fallen," verbal adjective from piptein "to fall," from PIE root *pet- "to rush; to fly." Related: Asymptosy.