Here is the approximate pecking order of the English caste system, compiled from various sources.

 I. SOVEREIGNTY
      king, queen
      prince, princess

II. SUBJECTS
    A. ECCLESIASTICAL (CLERGY)
    B. STATES
       1. MILITARY
          General: originally meant to be of similar 'birth' or 'class' with the sovereign;
                   the more recent use is to be familiar with all facets of the army, no longer
                   a specialist in one area, a 'general officer'.
          Colonel: an officer commanding a 'column' of soldiers and support trains.
          Captain: an officer entrusted with a command or fort under a sovereign or general.
          Lieutenant: an officer representing and exercising powers on behalf of his lord or
                      sovereign.
          Sergeant: servant; attendant upon a knight in the field.
          Corporal: influenced by 'corps'; head, chief.
          Private: having attained no title of rank, a 'private soldier'.
       2. MARITIME
       3. CIVIL
          a. Nobility (peerage, sometimes called "high nobility".)
               i.  Duke
              ii.  Marquis
             iii.  Earl, Count
              iv.  Viscount
               v.  Baron
                     lord or nobleman; the most general title of nobility in England;
                     judge of the court of exchequer
                     vassel holding directly from the king
          b. Dignity (degrees of honor, sometimes called "low nobility" though not nobility)
               Knights Baneret, created by sovereign in person on field of battle.
                    Can lead vassels into battle under his own banner.
               Knight (not hereditary), a soldier, assistant to a superior
                    commonly in return for land, "sir", a mounted man of arms serving a superior
                    Knights of the Garter, a/k/a Knights of the Order of St. George.
                 Baronet, granted by patent, lowest hereditary dignity or degree
                    of honor but not a title of nobility, baronets are commoners.
                 Knights Baneret, created by sovereign NOT in person; on field of battle
                    can lead vassels into battle under his own banner.
                 Knights of the Bath (took a bath the night before his creation.)
                    The order originally consisted of the sovereign, grand master,
                    and 36 knights companion.
                 Knights Bachelors (the lowest, but most ancient of the ranks of knight.)
                 Knights of the Chamber (title awarded in sovereign's chamber in peacetime.)
               Esquire
                  title of office for sheriffs, serjeants, barristers at law, justices,
                  and others.
               Gentleman
                  One without title, but with a coat of arms showing ancestry
                  A person of superior birth, above a yeoman.
               Yeoman
                  yeoman, freeholder, a man freeborn, butler for nobility,
                  gentleman attendant in royal household, "young man".
            c. Peasant
                  serf, countryman, tiller of the soil, laborer.

Other terms:

   NOBILITY, depends on context. If no discernable context or a legal context, then
             "nobility" only refers to duke, marquis, earl, viscount, and baron. In a non-legal
             context lower ranks are sometimes called low nobility while the upper ranks are
             called high nobility. Sometimes "nobility" includes both high and low nobility.

   SQUIRE short for esquire
   GENTRY of noble birth
   GENTLEMAN can refer to all of the nobility.
             Its meaning depends on the context in which it is used.
   PEER
     A nobleman; as a peer of the realm; the House of Peers, so
     called because noblemen and barons were originally
     considered as the companions of the king.

     In England, persons belonging to the five degrees of
     nobility are all peers [members of the peerage.]

   CITIZEN
     1. The native of a city, or an inhabitant who enjoys the freedom
        and privileges of the city in which he resides; the freeman
        of a city, as distinguished from a foreigner, or one not
        entitled to its franchises.
     2. A townsman; a man of trade; not a gentleman.
     3. An inhabitant; a dweller in any city, town or place.
     4. In a general sense, a native or permanent resident in a city
        or country; as the citizens of the United States.
     5. In the United States, a person, native or naturalized, who has
        the privilege of exercising the elective franchise, or the
        qualifications which enable him to vote for rulers, and to
        purchase and hold real estate.

        "If the Citizens of the United States should not be free and happy,
        the fault will be entirely their own." --Washington