An Etymological Dictionary of Astronomy and Astrophysics

To change continually; to shift back and forth; vary irregularly; to rise and fall in or as if in waves.

Etymology (EN): From L. fluctuationem (nom. fluctuatio), from fluctuare “to undulate,” from fluctus “wave,” from p.p. of fluere “to flow.”

Etymology (PE): Verbal form of oftâxiz, → fluctuation.