In reduplication new words are made by doubling a stem, either without any phonetic changes as in bye-bye (coil, for good-bye} or with a variation of the root-vowel or consonant as in ping-pong, chit-chat (this second type is called gradational reduplication).
This type of word-building is greatly facilitated in Modern English by the vast number of monosyllables. Stylistically speaking, most words made by reduplication represent informal groups: colloquialisms and slang. E. g. walkie-talkie ("a portable radio"), riff-raff ("the worthless or disreputable element of society"; "the dregs of society"), chi-chi (sl. for chic as in a chi-chi girl).
In a modern novel an angry father accuses his teenager son of doing nothing but dilly-dallying all over the town.
(dilly-dallying — wasting time, doing nothing, loitering)
Another example of a word made by reduplication may be found in the following quotation from The Importance of Being Earnest by O. Wilde:
Lady Bracknell. I think it is high time that Mr. Bunbury made up his mind whether he was going to live or to die. This shilly-shallying with the question is absurd.
(shilly-shallying — irresolution, indecision)