From PIE *pleh₂- (flat, broad) — 'field' spread from open plains into battlefields, force fields, and fields of study.
An area of open land, especially one used for agriculture or pasture. Also used for an area of study, a battlefield, or a region of physical force.
From Old English 'feld,' meaning open land, plain, pasture, from Proto-Germanic *felthuz (flat, open land), from PIE *pleth₂- (flat, broad, to spread), the same root that gives 'flat,' 'floor,' 'place,' 'plaza,' 'piazza,' 'plate,' 'platform,' and 'platitude.' The semantic core is flatness and openness — a field is fundamentally a flat expanse. The PIE root *pleth₂- is remarkably productive: through Latin 'planus' (flat) it yielded 'plain,' 'plane,' 'plan,' 'planet' (a 'wandering' star, from Greek 'planetes,' but influenced