By the way, it’s not likely that you’ll get a response from Cecil in this forum. You’ll have to make do with the rest of us.
As prior posters have said, traditionally an “attorney” is a representative who is empowered to act on your behalf. An “attorney at law” is someone who acts for you on legal matters. In almost all jurisdictions, an attorney at law must be a “lawyer” (someone licensed to practice law). The vast majority of attorneys are attorneys at law, but there are some cases in which attorneys need not be an attorney at law.
Lawyer - A person licensed to practice law
Advocate - A person who speaks on behalf of another person. In a court of law, your advocate will be your lawyer and will be an attorney at law. In English, “advocate” is a common synonym for “lawyer,” but rarely has any official meaning.
Counselor - A person who gives you advice. In English “counselor” is a common synonym for “lawyer,” but rarely has any official meaning. However, there is (or was) a state (South Carolina?), where the term “counselor” was an official title granted to senior lawyers, kind of like king’s/queen’s counsel in Britain. In fact, the Irish equivalent of a Q.C. is senior counsel. In court, a judge will address your lawyer/attorney as “counsel.”
Solicitor - In the British system, a solicitor is traditionally a lawyer who represents clients, but is not allowed to plead at the bar in the highest courts. (This has changed to a great extent, and solicitors now are able to argue in many courts.) A solicitor is called a “solicitor advocate” when arguing in court.
Barrister - In the British system, a barrister is a lawyer who may plead at the bar in the highest courts. Barristers may not take on clients directly. They are “instructed” by a party’s solicitor and are paid by the solicitor, not by the client. Barristers are not attorneys and may not act for a client other than arguing in court.
This solicitor/barrister split actually spawned varying terminologies in different courts (which I can’t remember exactly)–
Court of law (common law) – attorney at law/?
Court of equity (chancery) – solicitor/?
Admiralty/ecclesiastical/probate/divorce court – proctor/?
Scottish courts – solicitor/advocate
An agent. Someone who represents you and is not an attorney at law.
That’s up to the law of the specific jurisdiction. So far as I know, most common law jurisdictions require judges to be licensed lawyers. However, in civil law jurisdictions, I believe that lawyers and judges follow different paths of training.