Source : Webster's Revised Unabridged Dictionary (1913)

Tepal \Tep"al\, n. [F. t['e]pale, fr. p['e]tale, by
   transposition.] (Bot.)
   A division of a perianth. [R.]

Source : WordNet®

tepal
     n : an undifferentiated part of a perianth that cannot be
         distinguished as a sepal or a petal (as in lillies and
         tulips)