We have seen this word as diacritical term "accent aigue".
e.g. "é". But in next to last chapter, one of the villains
is described as having "lemon peel eye" (meaning his is jaundiced)and feverish, and Long John Silver menitons his have had "ague".
ague (pronounce a gyew)
n.
5ME < OFr ague < ML (febris) acuta, violent (fever): see ACUTE6
1 a fever, usually malarial, marked by regularly recurring chills
2 a chill; fit of shivering
a[gu[ish 7a4gy1 i*8
adj.