Pick an accesible online dictionary. Then use a pattern like the following: - Lookup the definition of the word for the day. Take the first word in the definiti

Pick an accesible online dictionary. Then use a pattern like the following: - Lookup the definition of the word for the day. Take the first word in the definition. - Lookup the definition of that word. Take the first word in its definition. - Repeat, maybe? - Use the first word in the definition as the key. Easy to verify but hard to reverse.