As I was reading Old Mortality by Sir Walter Scott, I came across the following words, which sent me to the dictionaries and the encyclopedias.
A man mentioned in the Bible in the Book of Joshua in connection with the fall of Jericho and conquest of Ai. (Wikipedia)
The doctrine that the state is superior to the church in ecclesiastical matters. It is named after the 16th-century Swiss physician and Zwinglian theologian Thomas Erastus, who never held such a doctrine. (Encyclopaedia Britannica)
A spring onion (Dictionary.com)
A mounted sentry in advance of the outposts of an army. (The Free Dictionary)