Although most Korean dictionaries regard e.g. ``talkatak`` and ``asasak`` as related to ``talkak`` and,. asak`` by reduction, some linguists regards the latter as the base and derives the former by extension with `` -tak`` (talkak>*talkak-tak>talkatak) or partial reduplication (asak>*asak-sak>asasak). Shin (1998: 35), for example, derives ``kachicak`` from ``kachil-cak`` with /1/ elided before the coronal /c/, while Lee (1998: 149-150) relates, e.g. ``rnancak`` to ``rnancicak`` by ``coalescence``, which drops the medial syllable / cij. Such conflicting views call for a systematic reanalysis of Korean sound symbolic word formation, which this paper presents in three patterns of extension and reduction: 1) morphological extension, e.g. talkak>``talkak-tak>talkatak; 2) morphological reduction, e.g. *okil-sikil>oksikil; 3) phonologial reduction by syncope, e.g. alisolJ > als``olJ. These patterns of extension and reduction, though previously overlooked, show a wellorganized interaction between morphology and phonology.