From The Collaborative International Dictionary of English v.0.48:
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.
[1913 Webster]
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.
[1913 Webster]