"Injunct" vs "Enjoin"

Language changes. That's why we're not speaking Old English anymore. Perhaps the people using "to injunct" feel it's clearer and more natural than "to enjoin".

That said, Google ngrams shows the following:

There appears to be a decline in the use of "enjoin" overall, but no use of "injunct" at all. I can't find any uses of "injunct" in the Corpus of Contemporary American English either. So I think it's safe to say that "injunct" will be considered an error for some time.

I think it's far too late to stop the "illegitimate back-formation" injunct from being used as a word. The question of whether/when others will accept this usage is subjective, but for myself I have no problem with it and I think OP's position is peevish.

This NGram shows over a thousand written instances from the second half of the last century, with usage apparently increasing. I would expect there to be far more this century, given the flurry of media interest in legal injunctions over recent years.

I assume the reason @Mr. Shiny and New found no instances of the verb form was because he searched for the present participle/infinitive injunct. Many speakers will sense that there is/was something "not quite right" about the usage, so it's no surprise they still shy away from the bare uninflected form. In any case, most references would naturally be in the past tense, since there's not much reason to write about the activity until it's actually happened.

OP seems to imply that the "purity" of English is somehow defiled by this neologism. Presumably because he has qualms about the "parentage", but I feel this gives the word something of the vibrance and vigour of a mongrel dog.

It will probably remain firmly entrenched in the semantic space surrounding legal injunctions, a term we're bound to be familiar with anyway. So we have an excellent new word available to cover exactly that context, that requires no effort at all to "learn". I only wish all neoligisms were this easy to assimulate into, and thus enrich, our beautiful ever-changing language.