It seems that the word cumin has never been etymologized. It derives from a Near-Eastern source through Latin and Greek. Greek κύμινον itself seems to share a triliteral root kmn with a number of Semitic languages, for example Old Akkadian kamūnum, or Arabic kamūn كَمُون. This can be shown to be an illusion. This plant comes from Central Asia where it is frequently called the ‘black seed’: Tadjik siyoh dona (‘black seed’) or Hindi kala jeera (‘black cumin’).
There exists an Afrasian root *km ‘black’. It can be found in Hieroglyphic Egyptian: km ‘black’, Coptic kmom ‘to become black’, hence a Feminine form km-t for the earth, the mud that Egyptians farmers used to till, and by metonymy Egypt itself: Coptic kême, from an ancient vocalic scheme *kūmat. It must be noted that the skeleton kmn of Greek is an illusion because κύμινον is in fact a base κύμ- suffixed by -ινον, a productive suffix that exists in other lexemes like σέλινον ‘parsley’. In that paradigm of plant names accent falls regularly on the first syllabe. What must be explained is therefore only the base *kum, for the suffix -ινον is Greek. The origin of the base can be found in Aramean (ˀa)kūm ‘black’. Both names are attested in Mycenian Greek: ku-mi-no and se-ri-no. The third nasal is identical by chance coincidence because Semitic words are independent derivatives of the root *km ‘black’.