Etymology Dictionary

JOG,  to push slightly, jolt.  (C.)   M.E. joggen, juggen.   'And him she joggeth;' Chaucer, Legend of Good Women, 2705.   'And Iugged til a iustice' (Trin. MS. iogged to a Iustice); P. Plowman, B. xx 133, where it is used of riding in a jolting manner.—W. gogi, to shake, to agitate; gogis, a gentle slap.   Cf. Irish gog, a nod of the head; gogaim, I nod, gesticulate; Gael. gog, a nodding or tossing of the head.   Cf. Gk. κυκάειν, to stir up, to mix up.   β. From ✔KAG, weakened form of ✔SKAG, to shake; whence W. ysgogi, to wag, stir, shake, ysgog, a quick motion, and E. shog, as used in Hen. V. ii. 1. 47.   See Shake.   Der. Hence jog as a neuter verb, to move by jolts, ride roughly, trot, Wint. Ta. iv. 3. 132, Tam. Shrew, iii. 2. 213; jog-trot; jogg-le, frequentative form.   ➩ Note that the connection with shake is only an ultimate one.

ADDENDA

Jog may be a mere corruption of shog, though it makes but little difference.   We actually find j for initial sh in the form jeltron, put for sheltron, a shelter, or shield, in Hickscorner; Dodsley's O. Plays, i. 149.