nabla

noun

nab·​la

ˈnablə

plural -s

1

: an ancient stringed instrument probably like a Hebrew harp of 10 or 12 strings

called also nebel

2

[probably so called from the resemblance of its symbol, the inverted Greek delta, to a harp] : an operator upon a function of three variables (as x, y, and z) interpreted as coordinates in a right-handed rectangular system for obtaining the partial derivatives of the function, for multiplying these derivatives by the unit vectors (as I, J, K) along the axes, and for adding the results

Word History

Etymology

Greek, of Semitic origin; akin to Hebrew nēbhel harp

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