jamyoudaoicibaDictYouDict
jam: [18] The verb jam, meaning ‘press tightly together’, first appears in the early 18th century (the earliest-known unequivocal example of its transitive use is in Daniel Defoe’s Robinson Crusoe 1719: ‘The ship stuck fast, jaum’d in between two rocks’). It is not known where it came from, but it is generally assumed to be imitative or symbolic in some way of the effort of pushing.

Equally mysterious are the origins of jam the sweet substance spread on bread, which appeared around the same time. Contemporary etymologists were nonplussed (Nathan Bailey had a stab in the 1730s: ‘prob. of J’aime, i.e. I love it; as Children used to say in French formerly, when they liked any Thing’; but Dr Johnson in 1755 confessed ‘I know not whence derived’); and even today the best guess that can be made is that the word refers to the ‘jamming’ or crushing of fruit into jars.
marzipanyoudaoicibaDictYouDict
marzipan: [19] The word marzipan has long puzzled etymologists. An elaborate theory was formulated in the early 20th century that traced it back to Arabic mawthabān ‘king who sits still’. That was applied by the Saracens to a medieval Venetian coin with a figure of the seated Christ on it. A series of fairly implausible semantic changes led from ‘coin’ via ‘box’ to ‘confectionery’, while the form of the word supposedly evolved in Italian to marzapane.

This turns out to be completely wide of the mark (not surprisingly), but the truth seems scarcely less remarkable. In Burma (now Myanmar) there is a port called Martaban, which was renowned in the Middle Ages for the jars of preserves and fruits exported from there to Europe. The name of the place came to be associated with its products, and in Italian, as marzapane, it denoted a type of sweetmeat (-pane for -ban suggests that some people subconsciously connected the word with Italian pane ‘bread’). Marzapane and its relatives in other languages (such as early modern French marcepain) entered English in the 16th century, and from the confusion of forms the consensus spelling marchpane emerged.

This remained the standard English word for ‘marzipan’ until the 19th century, when marzipan was borrowed from German; this was an alteration of Italian marzapane, based on the misconception that it came from Latin marci pānis ‘Mark’s bread’.