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I see Unicode expresses the character symbols as simply '[BLACK] UP-POINTING TRIANGLE' etc, but are there any single-word or 'catchier' terms for these orientations of triangles?

▲ △ -- up-pointing (U+25b2 and U+25b3)
▼ ▽ -- down-pointing (U+25bc and U+25bd)

It is to be used inside a figure caption, and the symbols represent location markers on a map. I use up and down-pointing triangles for the simple reason that I can overlay them, and produce a third symbol (6-pointed star) very easily.

I suppose I could do the same with a square and a diamond, and wouldn't have to think up a new word!

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    Personally, I just repeat whatever symbol I use in the figure caption. That way, no naming is necessary.
    – terdon
    Commented Oct 9, 2013 at 4:56

1 Answer 1

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Given that these are typographic symbols, they are implicitly two dimensional, so these terms should be understandable in that context:

▲ △ pyramid

▼ ▽ inverted pyramid

The pyramid oriented symbol also is known as the greek letter delta.

The inverted pyramid is used in mathematics as the gradient operator (and Hamiltonian operator), commonly called del, and formally called nabla.

Nabla is from the greek word for a hebrew harp, which has a similar shape. In The History of Nabla, its use as a mathematical symbol is discussed. It is also known as the Hamiltonian operator. Mathematician William Hamilton suggested the symbol be called "atled", which is "delta" spelled backwards. Clearly, the stratospheric thinkers of the times could not come up with any other terms (other than "nabla", which was itself referred to as a "humorous" proposal attributed to James Clark Maxwell).

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  • @terdon Err I think NAMBLA is something else...
    – user24964
    Commented Oct 11, 2013 at 10:29
  • Oops! And I wish I never heard of it. Commented Oct 11, 2013 at 12:51
  • @TheMathemagician I take it you were talking to Jim? Unfortunately now I know what NAMBLA is as well.
    – terdon
    Commented Oct 11, 2013 at 13:28
  • Oops sorry yes. Obviously not South Park fans.
    – user24964
    Commented Oct 11, 2013 at 15:18

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