Source : Webster's Revised Unabridged Dictionary (1913)

Truism \Tru"ism\, n. [From {True}.]
   An undoubted or self-evident truth; a statement which is
   pliantly true; a proposition needing no proof or argument; --
   opposed to falsism.

         Trifling truisms clothed in great, swelling words. --J.
                                                  P. Smith.

Source : WordNet®

truism
     n : an obvious truth