From The Collaborative International Dictionary of English v.0.48 [gcide]:
Del \Del\, n. [See Deal, n.]
Share; portion; part. [Obs.] --Chaucer.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
del \del\ n. (Math.)
a differential operator which, operating on a function of
several variables, gives the sum of the partial derivatives
of the function with respect to the three orthogonal spatial
coordinates; -- also called the gradient or grad. It is
represented by an inverted Greek capital delta ([nabla]), and
is thus because of its shape also called nabla, meaning
harp in Hebrew.
[PJC]