There are many reports on the origin of the term Mmadụ in the Igbo Language. Mmadu can be translated to Human in English but this is just for the lack of a proper alternative. Mmadụ, as Igbos perceived it, is something far higher than mere flesh. Of all of I have read about the origin of that term, 2 was outstanding.
One said that Igbo traditional religion has a lot of reverence for life which they call ndụ. Hence, their excessive usage of the idiom Ndụ Mmiri, Ndụ Azụ (Metaphorical supplication for the preservation of life). And every serious sacrifice, depending on its magnitude, requires a life. The greatest of all the sacrifices was human sacrifice, because they believed that there was nothing greater than human beings. From these props, one group of scholars believe that man, in Igbo spiritualism, is the beauty of life (mma ndụ - literally meaning beauty of life). And for that reason, humans are called Mmadụ.
The second group takes it to another philosophical level and below is the summary of the submission:
In Igbo cosmology, spirits are referred to as Mmuo (spirits) and from creation, the greatest spirits of this universe are - Mmou Ọnwụ (Dead Spirit) and Mmou Ndụ (Living Spirit). Mmou Ndụ would always become Mmụọ ọnwụ and Mmụọ ọnwụ could reincarnate into Mmụọ Ndụ.Like every tongue on earth, Igbos have a way of pronouncing names or terms with no patience. Take my name for example, my siblings call me Oziaa (fast way of saying Ozioma), and my elder brother, we call Chiooe (that's Chigozie).Mmụọ Ọnwụ (The Dead Spirit) was not spared. Some tongues call it Mmụọ and others are still patient enough to pronounce Mmanwụ.
Mmụọ Ndụ (The Living Spirit) sounded as Mmadụ, and this becomes its term till today. However, the arts of the ancient Igbo always marry both.
That's why shrines always have a drawn representation of the living and the scary face of the dead. And Igbo, in every speech, will always join both.