momentarily (adv.)

1650s, "for a moment," from momentary + -ly (2). Meaning "at any moment" is attested by 1928.

momentarily, momently. The first means for a moment (he was momentarily abashed), the second from moment to moment or every moment (am momently expecting a wire from him). The differentiation is well worth more faithful observance than it gets; & the substitution of either, which sometimes occurs, for instantly or immediately or at once is foolish novelty-hunting. [Fowler, 1926]