*kakka- Look up *kakka- at Dictionary.com
also kaka-, Proto-Indo-European root meaning "to defecate." According to Watkins, "imitative of glottal closure during defecation."

It forms all or part of: caca; cachexia; caco-; cacoethes; cacophony; cucking stool; kakistocracy; poppycock.

It is the hypothetical source of/evidence for its existence is provided by: Greek kakke "human excrement," Latin cacare, Irish caccaim, Serbo-Croatian kakati, Armenian k'akor; Old English cac-hus "latrine."

Etymologists dispute whether the modern Germanic words (Dutch kakken, Danish kakke, German kacken), are native cognates or student slang borrowed from Latin cacare. Caca appears in Modern English in slang c. 1870, and could have been taken from any or several of the languages that used it.