Ben Yagoda compares words whose definitions have shifted over time:
Presently has gone from "shortly" to "currently"; momentarily from "for a moment" to "in a moment"; and nonplussed from perplexed to unimpressed, or fazed to unfazed.
Should we acquesce to newer meanings when they are obviously less clear than what they replaced?
Balancing the possibility that you'll confuse your audience, and the prospect of appearing pretentious or dorky, is the chance that the old meaning could be a really good meaning, which no other word conveys precisely. There is no exact synonym for (the old-fashioned) disinterested, for example. In such cases, keeping a "legacy" sense in circulation is laudable activism in pursuit of semantic sustainability—as if you found some members of a near-extinct species of mollusk and built a welcoming environment in which they could breed.
And that's not the same as being merely a linguistic scold. I miss the words "gay" and "queer", for example, in their original meanings. I say that not as a homophobe, but as a lover of Anglo-Saxon English, in all its polyglot bluntness. I hope that future generations will not find Shakespeare or the Book Of Common Prayer unintelligible or, worse, meaning things they did not mean.