perturbation
per.tur.ba.tion \.p*rt-*r-'ba--sh*n, .p*r-.t*r-\ \-shn*l, -sh*n-*l\ n 1: the action of perturbing : the state of being perturbed 2: a disturbance of the regular elliptic or other motion of a celestial bod y produced by some force additional to that which causes its regular motion - per.tur.ba.tion.al aj