In the way they employ language, lawyers are like scientists. They use words in specific, closely-defined ways that laypeople often misuse or misunderstand. Take the four terms flotsam, jetsam, lagan and derelict, a euphonious collection from the law of the sea that sounds like a Groucho Marx firm of lawyers. We may think that we know the meanings of all these — apart from the rare and specialist lagan — but lawyers and seafarers will tell us differently.
Many people are confused about the difference between flotsam and jetsam, one idea being that flotsam is goods that float on the sea while jetsam is goods that have washed up on the beach. This confusion can be traced back to the sixteenth century because of a misunderstanding of the wording of a law. Any shipwrecked goods that reach the shore are instead legally called wreck. It’s also often assumed that they’re much the same thing, which is why the two words have become the set phrase flotsam and jetsam:
What might seem to be the material flotsam and jetsam of everyday life, for some people is emblematic of the process of change. It is collected as an outward reassurance to oneself and a testimony to the world that they have existed.
The Independent, 26 Jul. 2011.
Lawyers make a subtle distinction between them. Flotsam (from the Anglo-Norman floteson, connected to our float and to late Latin flottare, to float) is goods from a ship that has sunk which can be recovered because they remain afloat; jetsam (a variant form of English jettison formed by association with the slightly older flotsam) is goods that have been deliberately thrown over the side of a ship in an emergency to lighten it and so save it from shipwreck.
Of the other two, derelict in this context has a technical sense of goods that have sunk to the seabed, can’t be retrieved and are regarded as having been abandoned by their owner. Lagan — which derives from Old French but may be linked to an Scandinavian word associated with English lie and lay — also refers to goods or wreckage that has sunk to the seabed, but marked, usually with a buoy, so it can be retrieved later.