Lewis & Short

singultim. adv. [from singultus; cf.: furtim, partim, etc.], sobbingly: μετά λυγμοῦ, Hor. S. 1, 6, 56 (others less correctly make it = singulatim, singillatim, singly): lamentabiles questus singultim instrepebat, App. M p. 127, 36.