In Cape Verde, the Afro-Portuguese Creole of the island of Santiago, the so-called Badew, displays many contrastive verb-noun pairs in which the verb is characterized by a mid-open vowel, and the noun by an open one. The origin of this phenomenon has a historical explanation, in this case a stress-shift (from the last-syllable to the penultimate one) of the verb-word (derived from the oxytonic Portuguese infinitive), due to a dominant /'CVCV/ pattern in Badew. Nevertheless, in modern Badew, diachrony does not account for all the verb-noun pairs based on the opposition between mid-open and open vowels. This opposition has become a morphological device that enables Badew to derive new nouns from verbs and vice-versa. Considering the fact that Badew is a Creole language, the appearance of this new derivational system, inexistant in Portuguese, the lexifier language, could have been favored by the necessity of compensating for the failures and ambiguities of a poor vocabulary inherited from the pidgin stage of the language.