stadard unit of English long measure, Middle English yerd, from Old English gerd (Mercian), gierd (West Saxon) "rod, staff, pole, stick;" also a measure of length," from Proto-Germanic *gazdjo "stick, rod," reconstructed to be from PIE root *ghazdh-o- "rod, staff, pole" (source also of Latin hasta "shaft, staff").
The nautical yard-arm, a long spar tapered at both ends and lashed to the mast of a ship from which certain sails are suspended, retains the otherwise obsolete original sense of "rod, staff." Yard in the nautical sense is by late 13c. (as in man the yards and like expressions).
As a unit of length, in Anglo-Saxon times a land measure of roughly 5 meters (later called rod (n.), pole, or perch (n.1)). The yard measure of three feet is attested from late Old English. Especially by late 14c. as a standard measure for cloth (a rough equivalent for commercial measure was the ell of 45 inches, and the verge).
Middle English yerd (Old English gierd) also was "yard-land, yard of land," a varying measure but often about 30 acres or a quarter of a hide.
Germanic cognates include Old Saxon gerda, Old Frisian ierde, Dutch gard "rod;" Old High German garta, German gerte "switch, twig," Old Norse gaddr "spike, sting, nail."
The slang meaning "one hundred dollars" is attested by 1926, American English. In Middle English and after, the word also was a euphemism for "penis" (as in "Love's Labour's Lost," V.ii.676).
