The Collaborative International Dictionary of English v.0.48:

Rank \Rank\ (r[a^][ng]k), a. [Compar. Ranker
   (r[a^][ng]k"[~e]r); superl. Rankest.] [AS. ranc strong,
   proud; cf. D. rank slender, Dan. rank upright, erect, Prov.
   G. rank slender, Icel. rakkr slender, bold. The meaning seems
   to have been influenced by L. rancidus, E. rancid.]
   1. Luxuriant in growth; of vigorous growth; exuberant; grown
      to immoderate height; as, rank grass; rank weeds.
      [1913 Webster]

            And, behold, seven ears of corn came up upon one
            stalk, rank and good.                 --Gen. xli. 5.
      [1913 Webster]

   2. Raised to a high degree; violent; extreme; gross; utter;
      as, rank heresy. "Rank nonsense." --Hare. "I do forgive
      thy rankest fault." --Shak.
      [1913 Webster]

   3. Causing vigorous growth; producing luxuriantly; very rich
      and fertile; as, rank land. --Mortimer.
      [1913 Webster]

   4. Strong-scented; rancid; musty; as, oil of a rank smell;
      rank-smelling rue. --Spenser.
      [1913 Webster]

   5. Strong to the taste. "Divers sea fowls taste rank of the
      fish on which they feed." --Boyle.
      [1913 Webster]

   6. Inflamed with venereal appetite. [Obs.] --Shak.
      [1913 Webster]

   Rank modus (Law), an excessive and unreasonable modus. See
      Modus, 3.

   To set (the iron of a plane, etc.) rank, to set so as to
      take off a thick shaving. --Moxon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ranker \Rank"er\ (r[a^][ng]k"[~e]r), n.
   One who ranks, or disposes in ranks; one who arranges.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ranker
    n 1: a commissioned officer who has been promoted from enlisted
         status
    2: an enlisted soldier who serves in the ranks of the armed
       forces