Source : Webster's Revised Unabridged Dictionary (1913)

Think \Think\, v. t. [imp. & p. p. {Thought}; p. pr. & vb. n.
   {Thinking}.] [OE. thinken, properly, to seem, from AS.
   [thorn]yncean (cf. {Methinks}), but confounded with OE.
   thenken to think, fr. AS. [thorn]encean (imp.
   [thorn][=o]hte); akin to D. denken, dunken, OS. thenkian,
   thunkian, G. denken, d["u]nken, Icel. [thorn]ekkja to
   perceive, to know, [thorn]ykkja to seem, Goth. [thorn]agkjan,
   [thorn]aggkjan, to think, [thorn]ygkjan to think, to seem,
   OL. tongere to know. Cf. {Thank}, {Thought}.]
   1. To seem or appear; -- used chiefly in the expressions
      methinketh or methinks, and methought.

Thinking \Think"ing\, a.
   Having the faculty of thought; cogitative; capable of a
   regular train of ideas; as, man is a thinking being. --
   {Think"ing*ly}, adv.

Thinking \Think"ing\, n.
   The act of thinking; mode of thinking; imagination;
   cogitation; judgment.

         I heard a bird so sing, Whose music, to my thinking,
         pleased the king.                        --Shak.

Source : WordNet®

thinking
     adj : endowed with the capacity to reason [syn: {intelligent}, {reasoning(a)},
            {thinking(a)}]

thinking
     n : the process of thinking (especially thinking carefully);
         "thinking always made him frown"; "she paused for
         thought" [syn: {thought}, {cerebration}, {intellection},
         {mentation}]