The word for "hand/hands" and "arm/arms" is the same in Swahili, "mkono/mikono", and there is a word for "palm/palms" ("kiganja/viganja") but I think this is less used in common conversations.
mkono (m-mi class, plural mikono)
3) A unit of length about half a yard long.
kiganja (ki-vi class, plural viganja)
1) palm (inner, concave part of hand)
Video tutorial #22 from Growing Opportunities International (GO!):
Maybe you don't need to add 'of the hand' but it shouldn't be counted wrong