English 'pilgrimage' comes through Old French from Late Latin 'peregrīnus' (foreigner, traveler), from Latin 'per' (through) + 'ager' (field) — a pilgrim was literally one who traveled 'through foreign fields,' a spatial metaphor that Christianity redirected from mere foreignness to sacred journeying.
A journey to a sacred place as an act of religious devotion, or any long journey undertaken for a deeply felt purpose.
From Old French 'pelerinage' (pilgrimage), from 'pelerin' (pilgrim), from Late Latin 'peregrīnus' (foreigner, traveler), from Latin 'peregrīnus' (foreign, from abroad), from 'peregr-' (abroad), from 'per' (through, beyond) + 'ager' (field, land, territory). A pilgrim was literally someone who traveled 'through the fields' — that is, through foreign territory. The shift from 'foreign traveler' to 'religious traveler' occurred in early Christianity, when the faithful journeyed to holy sites in Palestine. Key
The peregrine falcon gets its name from the same Latin 'peregrīnus' (foreign traveler) because it was traditionally captured during its migratory passage rather than taken from the nest. English 'acre' and Latin 'ager' (the land the pilgrim crosses) are cognates from PIE *h₂eǵros — so embedded in the word 'pilgrimage' is the very ground the traveler walks across.