Source : Webster's Revised Unabridged Dictionary (1913)

Understand \Un`der*stand"\ ([u^]n`d[~e]r*st[a^]nd"), v. t. [imp.
   & p. p. {Understood}, and Archaic {Understanded}; p. pr. &
   vb. n. {Understanding}.] [OE. understanden, AS. understandan,
   literally, to stand under; cf. AS. forstandan to understand,
   G. verstehen. The development of sense is not clear. See
   {Under}, and {Stand}.]
   1. To have just and adequate ideas of; to apprehended the
      meaning or intention of; to have knowledge of; to
      comprehend; to know; as, to understand a problem in
      Euclid; to understand a proposition or a declaration; the
      court understands the advocate or his argument; to
      understand the sacred oracles; to understand a nod or a
      wink.

Understand \Un`der*stand"\, v. i.
   1. To have the use of the intellectual faculties; to be an
      intelligent being.

            Imparadised in you, in whom alone I understand, and
            grow, and see.                        --Donne.

   2. To be informed; to have or receive knowledge.

            I came to Jerusalem, and understood of the evil that
            Eliashib did for Tobiah.              --Neh. xiii.
                                                  7.

Source : WordNet®

understand
     v 1: know and comprehend the nature or meaning of; "She did not
          understand her husband"; "I understand what she means"
     2: perceive (an idea or situation) mentally; "Now I see!"; "I
        just can't see your point"; "Does she realize how
        important this decision is?"; "I don't understand the
        idea" [syn: {realize}, {realise}, {see}]
     3: make sense of a language; "She understands French"; "Can you
        read Greek?" [syn: {read}, {interpret}, {translate}]
     4: believe to be the case; "I understand you have no previous
        experience?" [syn: {infer}]
     5: be understanding of; "You don't need to explain--I
        understand!" [syn: {sympathize}, {sympathise}, {empathize},
         {empathise}]
     [also: {understood}]