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Such terms are known as Reduplicated or Ricochet Words, and include:

Chit-chat, click-clack, clitter-clatter, dilly-dally, ding-dong, drip-drop, fal-lal, flim-flam, fiddle-faddle, flip-flop, fliffy-fluffy, flippity-floppity, handy-pandy, harum-scarum, helter-skelter, heyve-keyve (Halliwell), hibbledy-hobbledy, higgledy-piggledy, hob-nob, hodge-podge, hoity-toity, hurly-burly, mish-mash, mixy-maxy, namby-pamby, niddy-noddy, niminy-piminy, nosy-posy, pell-mell, pit-pat, pitter-patter, randem-tandem, randy-dandy, ribble-rabble, riff-raff, roly-poly, rusty-fusty-crusty, see-saw, shilly-shally, slip-slop, slish-slosh, snick-snack, spitter-spatter, splitter-splutter, squish-squash, teeny-tiny, tick-tack, tilly-valley, tiny-totty, tip-top, tittle-tattle, toe-toes, wee-wee, wiggle-waggle, widdy-waddy (Halliwell), widdle-waddle, wibble-wobble, wish-wash, wishy-washy

For their origins and definitions:

http://www.phrases.org.uk/meanings/reduplication.html
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