It
is a word I first learned from Shakespeare, but from 'Hamlet' :-
'Sir, in my heart there was a kind of fighting
That would not let me sleep. Methought I lay
Worse than the mutines in the bilboes.'
(Or something very similar to that).
The bilboes were apparently fetters in the form of an iron bar that both feet were shackled to. Hamlet is referring to the mutineers of the ship he is on, lying below deck in irons.
I meant literally 'in bonds.' Not like barrels before their release.
And looking it up confirmed that bilboes only exist in the plural form.
There is a single noun bilbo, but I think it means a sword.