asymptote (n.) Look up asymptote at Dictionary.com
"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" (see petition (n.)). Related: Asymptosy.