Words relating to hands are intertwined with an extraordinary number of phrases and descriptions in the English language. This makes it difficult to search the internet for hand related topics - a search for "hand" also retrieves handicap, handmade, handy, handbook, etc. The same ubiquitous multifaceted presence in English is true for each of these words: finger, thumb, nail, palm, hand, wrist, elbow. Where did these words come from? The historical origins detailed below are quoted from the Dictionary of Word Origins by John Ayto. "Old English" origins date before the Norman invasion of 1066. Interesting... word origins suggest that etymologically the the hand has five fingers, one of which is the thumb, that wrist is named for its twisting motion, but not because "wrist" rhymes with "twist", and that the origin of the word hand mysterious.
Finger: (Old English) Widespread among the Germanic languages (German, Swedish and Danish all have finger, and Dutch vinger), finger is not found in any other branch of Indo-European. It is usually referred to a prehistoric Indo-European ancestor pengkrós 'number of five', a derivative (like fist) of pengke 'five'.
Thumb: (Old English) The thumb is etymologically the 'swollen' part - an allusion to its greater thickness than the other fingers. Along with its relatives German daumen and Dutch duim, it goes back to a prehistoric West Germanic thûmon. This in turn can be traced to Indo-European tum- 'swell', which also produced English tumour, and tumult. The b in thumb appeared in the early Middle English period, when it was still a two syllable word (thumbe), and at first was pronounced, but it has fallen silent over the centuries. The words thigh and thimble have related origins. 
Nail: (Old English) The Indo-European ancestor of nail was nogh- or onogh-. The latter was the source of Latin unguis (which evolved into French ongle and Italian unghia and has given English ungulate) and Greek ónux (source of English onyx). Both these strands refer only to the sort of nails that grow on fingers and toes, but the Germanic branch of the family (which has come from nogh- through a prehistoric Germanic naglaz) has differentiated into a 'fastening pin' - originally of wood, latterly of metal. Hence English nail and German nagel and Danish negl are used only for the anatomical 'nail'.
Palm: Palm the tree (Old English) and the palm of the hand (14th century) are effectively distinct words in English, but have the same ultimate source: Latin palma. This originally meant 'palm of the hand' (it is related to Irish lám 'hand' and Welsh llaw 'hand'), and the application to the tree is a secondary one, alluding to the shape of the cluster of palm leaves, like the fingers of a hand. The Latin word was borrowed into the Germanic dialects in prehistoric times in the tree sense, and now is wide spread (German palme and Dutch and Swedish palm as well as English palm). English acquired it in the 'hand' sense via Old French paume, with subsequent reversion to the Latin spelling. 
Hand: (Old English) Hand is a widespread Germanic word (German, Dutch and Swedish also have it), but has no relatives outside Germanic, and no one is too sure where it comes from. Perhaps the likeliest explanation is that it is related to Gothic frahinthan 'seize', 'pursue', Swedish hinna 'reach' and English hunt, and that its underlying meaning is 'body part used for seizing'. The derived adjective handsome (15th century) originally meant simply 'easy to handle'. The modern sense 'attractive' did not develop until the late 16th century.
Wrist: (Old English) The wrist is etymologically the 'twisting' joint. The word goes back to prehistoric German wristiz, which also produced German rist 'instep, wrist' and Swedish vrist 'instep, ankle'. This was derived from the base writh-, whose wr- sound seems originally to have been symbolic of the action of twisting. Variants of the base lie behind Old English words wreath, wrest, and writhe.
Elbow: (Old English) Logically enough, elbow means etymologically 'arm bend'. It comes from a prehistoric West and North Germanic alinobogan (which also produced German ellenbogen, Dutch elleboog, and Danish albue). This was a compound formed from alinã 'forearm' and bogan (source of English bow). However, there is a further twist. For alinã (source also of Old English ell - a measure of length equal to that of the forearm) itself goes back ultimately to an Indo-European base el-, ele- which itself meant 'bend' and produces not just words for forearm (such as Latin ulna), but also words for 'elbow' (such as Welch elin). So, at this deepest level of all, elbow means tautologically 'bend bend'.