One of the central tactics of neo-obscurantist propaganda. It consists in subtly changing the meaning of a word, by using it with a different (or even opposite) meaning than its original one, in order to manipulate people to think and act in ways that go against their own ideals or interests.
On the short term, this tactic is used to promote or slander certain target people/ideas by arbitrarily labeling them with words/symbols with a strongly positive or negative connotation: since most people do not reason on concepts but only on their name/symbols, they most likely won't notice the trick and will be pushed to love or hate the target thing without ever checking whether it actually fits the attached label or not.
On the long term, the repeated use of this tactic can lead to a complete inversion of the original meaning of a word and, together with it, of the whole beliefs and behavior of their supporters or opposers.
In case some progressive (i.e.: empowering or emancipating) ideal becomes too widespread to be directly countered, if that ideal can be identified by a name or a symbol, then it can be "polluted" by introducing extraneous concepts into its definition (or by expunging integral parts of it), and this can go as far as to entirely invert the original meaning; for the reason explained above, the majority of supporters will unconsciously accept the new meaning in order not to "betray" it. In this way is it possible for propagandists to push regressive agendas by hiding them inside widely upheld progressive names/symbols, making them harmless of even useful for the establishment.
The same tactic can be used in the opposite way, that is: to introduce progressive meanings into widely reviled names/symbols, in order to either prevent people from supporting them, or forcing them to support both at the same time; the ultimate result is exactly the same as the one described above.
This tactic relies on the fact that irrational people tend to reason in terms of words and symbols rather than concepts; once a concept, or an ideal has been established as positive or negative, this acception will quickly be projected onto words and symbols standing for it, drawing attention away the original concept/ideal that can therefore be subtly changed or replaced with an opposite one without people noticing.
In other word, a word/symbol standing for a positive idea can be used as a "vector" to push harmful ones, and/or the other way around.
The trick for this tactic to work in the best possible way is that the new meaning of a word must never completely replace the original ones; rather, it should be allowed to coexist with it, so that the word becomes as equivocal and ambiguous as possible.
The reason is simple: if the meaning of a word gets simply flipped once and for all, people might eventually adapt to the new meaning and re-adjust their perception of it, and the word will quickly lose its manipulatory power. Instead, having many different incompatible meanings stay in a single word allows manipulators to switch between those meanings at will depending on the circumstances, to manipulate audiences in any way they want without them noticing.
This kind of ambiguity is also useful for another reason: it compromises proper communication and rational debate, encouraging internal infighting among the opposition and splitting it into factions.
The combined use of these tactics on a vast array of terms over a prolonged period of time can result in a complete subversion of vast portions of language, with obvious disastrous consequences for any kind of rational debate towards any kind of truth or social progress.