Although the word 'freight' can have several different meanings, where it comes from, or what language experts would call its entymology, is fairly straightforward.

Where the Meaning of 'Freight' is Derived From
The word is believed to have originated in late Middle English (an era roughly spanning the three centuries between the late 12th and the late 15th century), and meant 'hire of a ship for transporting goods.' The English word came about from the contemporary German/Dutch word vrecht, or vracht which meant 'ship's cargo.' This is similar to the origins of the word 'fraught,' as transporting large cargoes vast distances across the sea in those times was a hazardous business - transporting freight was fraught with danger! To learn more about the origins of the English language, watch this interesting BBC documentary: