Nabla symbol

∇

The nabla symbol

The nabla is a triangular symbol resembling an inverted Greek delta:^[1] $\nabla$ or ∇. The name comes, by reason of the symbol's shape, from the Hellenistic Greek word νάβλα for a Phoenician harp,^[2]^[3] and was suggested by the encyclopedist William Robertson Smith in an 1870 letter to Peter Guthrie Tait.^[2]^[4]^[5]^[6]^[7]

The nabla symbol is available in standard HTML as ∇ and in LaTeX as \nabla. In Unicode, it is the character at code point U+2207, or 8711 in decimal notation, in the Mathematical Operators block.

It is also called del.

^ Indeed, it is called anadelta (ανάδελτα) in Modern Greek.
^ ^a ^b "nabla". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ νάβλα. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
^ Letter from Smith to Tait, 10 November 1870:
My dear Sir, The name I propose for ∇ is, as you will remember, Nabla... In Greek the leading form is ναβλᾰ... As to the thing it is a sort of harp and is said by Hieronymus and other authorities to have had the figure of ∇ (an inverted Δ).
Quoted in Oxford English Dictionary entry "nabla".
^ Cargill Gilston Knott (1911). Life and Scientific Work of Peter Guthrie Tait. Cambridge University Press.
^ "History of Nabla".
^ Notably it is sometimes claimed to be from the Hebrew nevel (נֶבֶל)—as in the Book of Isaiah, 5th chapter, 12th sentence: "וְהָיָה כִנּוֹר וָנֶבֶל תֹּף וְחָלִיל וָיַיִן מִשְׁתֵּיהֶם וְאֵת פֹּעַל יְהוָה לֹא יַבִּיטוּ וּמַעֲשֵׂה יָדָיו לֹא רָאוּ"—, but this etymology is mistaken; the Greek νάβλα comes from the Phoenician to which נֶבֶל is cognate. See: "nable". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)