From Latin 'iter' (journey), from PIE *ei- (to go) — first applied to traveling judges and preachers.
Traveling from place to place, especially for work; a person who travels from place to place.
From Latin itinerantem, present participle of itinerārī (to travel, to make a journey), from iter (a journey, a road, a way, a march), genitive itineris. Iter derives from PIE *h₁ey- (to go), one of the foundational motion roots in the family: compare Sanskrit éti (goes), Greek eîmi (I go), Old Latin ire (to go), Lithuanian eĩti (to go). The same PIE root underlies Latin ire with its derivatives exit (a going out, from ex-ire), transit (a going across, from trans-ire), ambition (literally a going around to canvass
Medieval English 'justices itinerant' (justices in eyre) were royal judges who traveled a circuit to hold court in different towns, bringing the king's justice to places too distant from London. This practice, formalized in the twelfth century, is the direct ancestor of the modern circuit court system. The word 'itinerant' entered English legal vocabulary before it entered general