Intermittently; at intervals. Also, capricious, fickle. This nineteenth-century Americanism was originally a railroad term referring to minor mishaps, in which a train went off track and then back on again. It was reinforced by a popular song of about 1910, “Finnigin to Flannigan,” by Strickland Gillilan, which went, “Bilin’ down his repoort, wuz Finnigin! An’ he writed this here: ‘Muster Flannigan—Off agin, on agin, Gone again.—FINNIGIN.’” Today the term is frequently applied to romantic and other relationships characterized by intermittence. It is, of course, a version of off and on, current since the mid-nineteenth century.