to lie in such a dismal plash (pg. 176) -- A heavy rain.
No Gretna Green (pg. 199) -- A village in Scottland where many eloping couples are married.
coxcombery (pg. 300) -- Behavior that is characteristic of a coxcomb : foppery.
fanfaronade (pg. 300) -- Empty boasting.
sharks are mostly gammon (pg. 300) -- Misleading or nonsensical talk; humbug.
an unrivalled cholagogue (pg. 332) -- A cholagogue is a medicinal agent which promotes the discharge of bile from the system, purging it downward..
...a thunderous, long, long fart.
"I beg your pardon," said the midshipman in the silence.
"Oh, that's all right," said Diana coldly. "I thought it was the horse." -- pg. 46
creta alba (pg. 229) -- Chalk or calcium carbonate. There's a web site for this stuff at Master and Commander medical terms
barca-Longa (pg. 253) -- A two or three-masted lugger found on the coasts of Spain and Portugal as well as more widely in the Mediterranean Sea. And here I thought it was some kind of reclining chair!
membrum virile (pg. 345) -- Uh, penis.
squills (pg. 348) -- Sea squill is a bulb which sends up a tall stalk topped by an inflorescence of small white flowers, followed by a rosette of large dull green leaves, that last until the following summer. The bulb can get quite large, reaching over five pounds in weight.
States rights fetich (pg. 194) -- I know what a fetish is, and this is an alternate spelling, but its use seems odd in this context.
cumbrous (pg. 229) -- Cumbersome.
I believe in a graduated income tax on big fortunes, and in another tax--a graduated inheritance tax on big fortunes, properly safeguarded against evasion and increasing rapidly in amount with the size of the estate. (pg. 332)