tilde

also known as the 'swung dash'.

It's searchable online, but I believe you have to be a subscriber to use it. My employer is a subscriber and I use it frequently at work.

They do have an RSS feed (or is that redundant?) for a Word of the Day, which I've never used but it seems like it would be fun. Maybe I'll try it.

I stand corrected. I need to pick up the OED. Or is it searchable online?

I've always pronounced it "tildeh," or "tild-uh," as seanahan listed it. I have only ever known it as the symbol inkhorn cited so I can't speak to that usage, though OED lists its secondary meaning as "a symbol in Math. and Logic, chiefly to indicate negation."

Twiddle is a thing used in math. I've heard the pronunciations "tild", "tildee", and "tild-uh". I can't remember where I saw ~= used to be not equals, so I'll have to track it down. I've also seen ~ used to be about equals.

I always thought that use meant approximately, not not. Handwritten on paper you'd see one tilde drawn above another, to make a squiggly equals sign. It's the visual cue for for "fuzzy" equality, used when the answer is close to a given value but probably not exactly that value. Just like the analog counterpart to != is an equals sign with a slash through it, evoking a "no parking" symbol to nullify the operator. Then again, we all tend to draw symbols differently, and maybe use different visual cues; so I'm not saying you're wrong. I just haven't seen that before.

By the way, let's set the record straight... is it pronounced "tild" or "tildee?" Or "twiddle," which is another thing I've never seen before?

This symbol is used in various places as a "not" symbol, sometimes pronounced as "twiddle", with "~=" akin to "!=".

There's a cool article I happened to find and have no affiliation with whatsoever. http://diveintomark.org/archives/2002/10/04/history_of_the_tilde

Tilde Accent: jalapeño