1) They like to assign new meanings that are not merely inaccurate, but the opposite of what the term used to represent. "Patriot Act," "Deficit Reduction Act," "Environmental justice," etc.
2) Another method of making the terms corrupt is to corrupt the thing itself: "Department of Justice."
3) Create new terms which are lies when introduced: "ANTIFA" (of course, the term "anti-fascist" had already existed long before.
Emerson (From "Nature"): The corruption of man is followed by the corruption of language. When simplicity of character and the sovereignty of ideas is broken up by the prevalence of secondary desires, the desire of riches, of pleasure, of power, and of praise, -- and duplicity and falsehood take place of simplicity and truth, the power over nature as an interpreter of the will, is in a degree lost; new imagery ceases to be created, and old words are perverted to stand for things which are not; a paper currency is employed, when there is no bullion in the vaults.
Nice quotation from Emerson, thanks!