I cannot find "senectuous" as in "my senectuous bribee" page 235, Ishmael, Bantam/Turner trade paperback edition, in any dictionary. Please tell me what it means, and your authority.
...and the response from Daniel Quinn: "Senectuous" is a synonym for "elderly." It's formed from the word "senectitude" ("elderliness") in the same general way that "multitudinous" is formed from the word "multitude." There was a time when you couldn't find the word "chortle" in dictionaries; this is because didn't exist until Lewis Carroll invented it in 1872. You won't find "senectuous" in any dictionary for the same reason. It's a word I invented (a liberty taken by many authors).