A lot of Randians seem to think that the phrase and concept floating abstraction is specific to Rand; but in fact the term floating abstraction (or, more commonly, free-floating abstraction), often (though not always) meaning something actually fairly close to what Rand meant by it, is quite common in Continental and leftist thought, showing up in Marxist, feminist, phenomenological, and postmodernist discourse.
I dont know whether this is a coincidence or whether there was influence or, if so, in which direction. It would be interesting to know which came first, but Im not sure how old either version is. The oldest use I could find online for free-floating abstraction was from Kathleen Nott in 1969 (but I didnt search at much length); Rand was already using floating abstraction at least as early as 1961 (in For the New Intellectual) and probably earlier. (Its also in Brandens Principles lectures (as transcribed in The Vision of Ayn Rand), the earliest version of which was recorded in 1958, but I dont know which year the text in Vision comes from; and Atlas Shrugged seems to be working toward the concept in Galts reference to the words with rubber meanings, the terms left floating in midstream.)