borrowed from Greek, combining form from kakós "bad, of poor quality, worthless, low-born, unsightly," of uncertain origin
Note: R. Beekes (Etymological Dictionary of Greek, Brill, 2009) notes earlier comparisons of Greek kakós with Old Avestan kasu- "small, slight" (from Indo-European *kn̥ḱ-?) or alternatively with Lithuanian keñkti "to ache" and the base of Germanic *hungru- "hunger" (see hunger entry 1). Chantraine more circumspectly notes (Dictionnaire étymologique de la langue grecque): "as with many words meaning 'bad,' no established etymology. Originally a colloquial and expressive word" ("Comme beaucoup de mots signifiant 'mal', pas d'étymologie établie. Mot familier et expressif à l'origine").