复线

multiple track (e.g. rail) / multilane (e.g. highway) / (math.) complex line

to go and return / to return / to resume / to return to a normal or original state / to repeat / again / to recover / to restore / to turn over / to reply / to answer / to reply to a letter / to retaliate / to carry out

to repeat / to double / to overlap / complex (not simple) / compound / composite / double / diplo- / duplicate / overlapping / to duplicate

variant of 復|复[fu4] / to reply to a letter

variant of 線|线[xian4]

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

rifling (spiral lines on inside of gun barrel imparting spin to the bullet)