Just as some questions (e.g., Have you stopped bleating at your wife?) carry false presuppositions and so cant rationally be answered either yes or no, so some terms build false presuppositions into their meanings, making it impossible to use the term (at least in its ordinary sense) without signing on to the presupposition. (Racial and otherwise bigoted epithets are an obvious case.)
Rand used the term anti-concept to denote an unnecessary and rationally unusable term designed to replace and obliterate some legitimate concept; her favourite examples fall into the category of a package-deal of two meanings, with the proper meaning serving to cover and to smuggle the improper one into peoples minds.
I think I use the term slightly differently from the way Rand did; for one thing, I dont necessarily assume that such terms are always part of a purposeful design to corrupt thought and language. (I dont deny that they sometimes are; but I dont think Rand fully appreciated the power of spontaneous order, including malign spontaneous order on which see Charles Women and the Invisible Fist and my Invisible Hands and Incantations.)
Rand identified isolationism and extremism (inter alia) as examples of anti-concepts; Ive argued elsewhere that two of Rands own favourite virtue-terms selfishness and capitalism should likewise be treated, by her own standards, as anti-concepts.
Heres another Id like to add to the list: anti-Americanism. What is it to be an anti-American? It might mean any of at least four things: a) hostility to the American people and their interests, or b) hostility to the American government and its policies, especially its foreign policy and world role, or c) hostility to the founding principles of the u.s., most notably those embodied in the Declaration; or d) hostility to American culture and values.
Obviously theres no necessity for these four types of anti-Americanism to go together; on the contrary, they pull in different directions. Im pro-American in senses (a) and (c); and for precisely that reason Im anti-American in sense (b). As for sense (d), Im pro-American in some respects and anti-American in others, just as I would favour some aspects and oppose other aspects of just about any culture.
So whats the false presupposition, the package deal, in anti-Americanism? Its the tacit and illicit assumption that any person or position that is anti-American in sense (b) must also be anti-American in senses (a), (c), and (d). Thats how the term works; it builds into its very meaning a smear against critics of u.s. foreign policy. When people use it, call them on it!