With all due respect, this is a slight pet peeve of mine and the selected answer for this is actually wrong.
Granted language evolves, e.g., "google" is now a verb, apparently. Through what's known as "common use", it has earned its way into official dictionaries. However, "google" was a new word representing something heretofore non-existent in our speech.
Common use does not cover blatantly changing the meaning of a word just because we didn't understand its definition in the first place, no matter how many people keep repeating it.
The entire English-speaking computer industry seems to use "deprecate" to mean some feature that is being phased out or no longer relevant. Not bad, just not recommended. Usually, because there is a new and better replacement.
The actual definition of deprecate is to put down, or speak negatively about, or to express disapproval, or make fun of someone or something through degradation.
It comes from Latin de- (against) precari (to pray). To "pray against" to a 21st century person probably conjures up thoughts of warding off evil spirits or something, which is probably where the disconnect occurs with people. In fact, to pray or to pray for something meant to wish good upon, to speak about in a positive way. To pray against would be to speak ill of or to put down or denigrate. See this excerpt from the Oxford English Dictionary.
Express disapproval of:
(as adjective deprecating) he sniffed in a deprecating way
another term for depreciate ( sense 2).
he deprecates the value of children’s television
What people generally mean to convey when using deprecate, in the IT industry anyway, and perhaps others, is that something has lost value. Something has lost relevance. Something has fallen out of favor. Not that it has no value, it is just not as valuable as before (probably due to being replaced by something new.) We have two words that deal with concept in English and the first is "depreciate". See this excerpt from the Oxford English Dictionary.
Diminish in value over a period of time:
the pound is expected to depreciate against the dollar
Disparage or belittle (something):
Notice that definition 2 sounds like deprecate. So, ironically, deprecate can mean depreciate in some contexts, just not the one commonly used by IT folk.
Also, just because currency depreciation is a nice common use of the word depreciate, and therefore easy to cite as an example, doesn't mean it's the only context in which the word is relevant. It's just an example. ONE example.
The correct transitive verb for this is "obsolete". You obsolete something because its value has depreciated.
See this excerpt from the Oxford English Dictionary.
Verb - Cause something to be or become obsolete by replacing it with something new.
It bugs me, it just bugs me. I don't know why. Maybe because I see it everywhere. In every computer book I read, every lecture I attend, and on every technical site on the internet, someone invariably drops the d-bomb sooner or later. If this one ends up in the dictionary at some point, I will concede, but conclude that the gatekeepers of the English lexicon have become weak and have lost their way... or at the very least, lost their nerve. Even Wikipedia espouses this misuse, and indeed, defends it. I've already edited the page thrice, and they keep removing my edits.
Something is depreciated until it is obsolete. Deprecate, in the context of IT, makes no sense at all, unless you're putting down someone's performance or work or product or the fact that they still wear parachute pants.
Conclusion: The entire IT industry uses deprecate incorrectly. It may be common use. It may be some huge mis-understanding. But it is still, completely, wrong.
