The Burning Wheel has a character Trait called "He's a Jonah, that one" (BWG p.329). Like many character Traits in BW it has no further description. So what is the trait supposed to mean?
The answer is straightforward and you found it yourself: it means a person who brings bad luck (usually to a ship). It comes from the biblical story and is an old sailor expression/superstition.
The flowery title of the trait is just a dialog example of how a NPC sailor might accuse someone of being bad luck in-game.
There's a famous movie scene about a sailor constantly accused of being a Jonah. Spoiler alert if you have never watched Master & Commander.
A good idea with BW character Traits is to look, which Lifepaths have them as Lifepath Traits. The Lifepath Crazy Old Sailor has that Trait as a LP Trait alongside Superstitious and Metal Plate in the Skull (BWG p. 190). With that it is obvious that the Trait is referring to the second source more than the first. I see three plausible ways of interpreting it:
- Other people see the character as bad luck and say "He's a Jonah, that one" about him
- The character himself is prone to labeling random people as bringers of bad luck (plays of Superstitious)
- The character was literally swallowed up by a see monster and then spat back out (where do you think the plate in his skull come from).
This is clearly an allusion:
Allusion is a figure of speech, in which one refers covertly or indirectly to an object or circumstance from an external context. It is left to the audience to make the connection; where the connection is directly and explicitly stated (as opposed to indirectly implied) by the author, an allusion is instead usually termed a reference.
The trouble that you have is:
Without the hearer or reader's comprehending the author's intention, an allusion becomes merely a decorative device.
Well done for finding the references. I would guess that the author is using the Biblical allusion to the divinely inflicted bad luck of the prophet Jonah rather than a reference to a long-forgotten piece of slang from the 1950s. I suspect that the slang developed as a contronym from the original meaning of a person who brings bad luck to others; slang does this a lot, for example, "sick" and "wicked".
As an allusion it is up to the reader to divine what the author meant, however, in the phrase "He's a Jonah, that one" it seems pretty clear that the author is using the not strictly literal meaning of a person who brings bad luck to others by their presence (like the sailors on Jonah's ship until they chucked him overboard), rather than being a direct reference to the prophet himself.
These come up a lot - the only way to recognize them is to read more and follow up what you don't understand.