arm -a human limb; technically the part of the superior limb between the shoulder and the elbow but commonly used to refer to the whole superior limb.
In Bengali, there was a word for this part of the human body: Baahu. But today it is not in use. There is only word for arm and forearm- haat. If necessity arises to refer arm, we say "haater upor dik"or "haater uporibhaag"(the upper portion of hand).
It is interesting that a one single "sadhu" word replaced by three "chalit" words in colloquial language.