Not about italics for thought. Suppose I could have said that in the title. Sorry, the small troll that lives within couldn't resist. This is about the concept of introducing new terms in a world. I asked ChickenFreak who thought this may not be a needed moment for them in-spite of being a listed and suggested use. She advised that I ask. So I am. The word is "Leap" and its tenses. The idea is in my world people use this word to refer to an effect that can happen to people. Like a magical boast. People are either leaped or not. It could easily be something that might be listen on a license. Or a dictionary in my world may list a new meaning to the world leap. Something like; 1. Adjective, referring to a person who has went under a magical metamorphosis. Examples "Has Jane leaped yet?" "Jane is leaping!" "Jane has been a leaper for three years now." Should this use of the word leap be used in italics? Thank you for reading.
Leaped eh? Don't think it needs italics at all. As long as you don't go the Airbender route and end up with lines of dialogue like "oh no, here comes a bender!"
Introducing or defining terms, especially technical terms or those used in an unusual or different way:[6] "Freudian psychology is based on the ego, the super-ego, and the id."; "An even number is one that is a multiple of 2." - Source http://en.wikipedia.org/wiki/Italic_type It seems to be a valid use but is it a good use?
Magical metamorphosis isn't a defining term? Yeah not exactly like that but there is a moment where someone is under going a change and a character notices it. Like; "Oh look. The psychic is leaping. I never seen a leaped psychic before. This might be interesting." Is that like avatar? On reflection that is mainly because it is a short list of people that actually recognize it by sight. Usually it would have to be information the person said about themselves.
Just because you're redefining a word doesn't automatically mean it goes in italics. To be honest, this seems like an old rule and one that isn't followed very much today. Don't use italics; there's no need.
Only if it were being used in an academic paper. And then only for the first time of mention. In everyday life, the term would be used in its ordinary, non-academic sense. As in, "The butterfly went through metamorphosis to become the beautiful creature it is." Your examples about individuals "leaping," as the term is used in your world's parlance, are exactly right the way they are. No italics.