Literally, “out of the seven.” The beast itself—“the eighth”—was, it would seem, the same beast to which the seven heads had been attached (cf. ch. 13:11, 12). Absence in the Greek of the definite article before the word “eighth” suggests that the beast itself was the real authority back of the seven heads, and that it is therefore more than merely another head, the eighth in a series. It is their summation and climax—the beast itself. In the Greek the word for “eighth” is masculine and hence cannot refer to a head, the word for which is feminine.
Even he is the eighth.
Literally, “also himself is an eighth.” This is the beast in its revived state, in the “yet is” period following its ascent out of the “bottomless pit” (see on vs. 8, 10). Some consider the eighth power to be the papacy alone; others suggest that it represents Satan. Those who take the latter view point out that at the time here indicated Satan attempts to impersonate Christ (see on 2 Thess. 2:8).