LOIN (through O. Fr. loigne or logne, mod. longe, from Lat. lumbus), that part of the body in an animal which lies between the upper part of the hip-bone and the last of the false ribs on either side of the back-bone, hence in the plural the general term for the lower part of the human body at the junction with the legs, covered by the loin-cloth, the almost universal garment among primitive peoples. There are also figurative uses of the word, chiefly biblical, due to the loins being the supposed seat of male vigour and power of generation. Apart from these uses the word is a butcher's term for a joint of meat cut from this part of the body. The upper part of a loin of beef is known as the " surloin " (Fr. surlonge, i.e. upper loin). This has been commonly corrupted into " sirloin," and a legend invented, to account for the name, of a king, James I. or Charles II., knighting a prime joint of beef " Sir Loin " in pleasure at its excellence. A double surloin, undivided at the back-bone, is known as a " baron of beef," probably from an expansion of the legend of the " Sir Loin."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)