Old English gewiht "weighing, weight, downward force of a body, heaviness," from Proto-Germanic *wihti- (source also of Old Norse vætt, Danish vegt, Old Frisian wicht, Middle Dutch gewicht, German Gewicht), from *weg- (see weigh).
Figurative sense of "burden" is late 14c. To lose weight "get thinner" is recorded from 1961. Weight Watcher as a trademark name dates from 1960. To pull one's weight (1921) is from rowing. To throw (one's) weight around figuratively is by 1922. Weight-training is from 1945. Weight-lifting is from 1885; weight-lifter (human) from 1893.
"unit of money or weight," late Old English marc, a unit of weight (chiefly for gold or silver) equal to about eight ounces, probably from Old Norse mörk "unit of weight," cognate with German Mark and probably ultimately a derivative of mark (n.1), perhaps in a sense of "imprinted weight or coin." It was a unit of account in England into 18c., perhaps originally introduced by the Danes, but never the name of a particular coin.
The word is found in all the Germanic and Romanic languages (compare Old Frisian merk, Dutch mark, Medieval Latin marca, French marc (11c.), Spanish and Italian marco); in English it was used from 18c. in reference to various continental coinages, especially the silver money of Germany first issued 1875.