Hmmm... wiktionary includes a definition of "performant" as computer jargon meaning "capable of or characterized by an adequate or excellent level of performance or efficiency" [1]. I find it hard to disagree that this informal use has entered the computing lexicon (and don't personally object to it).
That "definition" includes eight distinct meanings. In time, any of them might be useful and the word might become an accepted part of the English language. For now, it just muddies the waters, when there are clear and unambiguous alternatives available. Perhaps that is why not one of the on- or off-line dictionaries I have just checked recognises any similar meaning of the word "performant".
This post has been brought to you by the "ironic parallels with the topic at hand" department.
> That "definition" includes eight distinct meanings.
"Performance" itself, and many other words, have lots of meanings [1].
> not one of the on- or off-line dictionaries I have just checked recognises any similar meaning of the word "performant"
True, but we have many terms in computing where our intended meaning is not captured by mainstream dictionaries.
> when there are clear and unambiguous alternatives available
Did you honestly find that usage unclear and ambiguous? The standard use of "performant" is so rare that there can be no doubt what the original poster meant. What are the alternative words you prefer? I think "performant" fills a gap.
> This post has been brought to you by the "ironic parallels with the topic at hand" department.
Nice observation! (perhaps not coincidently, I think I come down on the other side of the issue from you in both instances :)
[1] http://en.wiktionary.org/wiki/performant