1650s, "small pocket for valuables," probably related to Low German fobke "pocket," High German fuppe "pocket," "a dialectal word used in Livonia" [Klein]. Meaning "chain attached to a watch carried in the fob" is from 1885.
"to cheat," late 14c., from obsolete noun fobbe "cheat, trickster" (late 14c.), perhaps from Old French forbe "cheat" [OED]. Alternative etymology holds that the word is perhaps related to German foppen "to jeer at, make a fool of" (see fop); or from German fuppen, einfuppen "to pocket stealthily," which would connect it to fob (n.). To fob (someone) off is first recorded 1590s. Related: Fobbed; fobbing.