Source : Webster's Revised Unabridged Dictionary (1913)

Sepal \Se"pal\, n. [NL. sepalum, formed in imitation of NL.
   petalum, petal, to denote one of the divisions of the calyx:
   cf. F. s['e]pale.] (Bot.)
   A leaf or division of the calyx.

   Note: When the calyx consists of but one part, it is said to
         be monosepalous; when of two parts, it is said to be
         disepalous; when of a variable and indefinite number of
         parts, it is said to be polysepalous; when of several
         parts united, it is properly called gamosepalous.

Source : WordNet®

sepal
     n : one of the green parts that form the calyx of a flower