Meaning

noun a couple who both have careers and no children (an acronym for dual income no kids)

noun a soft return so that the tennis ball drops abruptly after crossing the net

originUncertain. Either: * A rhythmatic reduplicative of Chink, a derogatory term for a Chinese person. Attested from Australia since the 1960s (consult the American Heritage Dictionary). * or, clipping of dinky dau/dow, a corrupted borrowing from Vietnamese điên cái đầu (“[you make my] head goes crazy”).

Etymology from Wiktionary, CC BY-SA 3.0