Old English æcer "tilled field, open land," from Proto-Germanic *akraz "field, pasture" (cf. Old Norse akr, Old Saxon akkar, Old Frisian ekker, Middle Dutch acker, Dutch akker, Old High German achar, German acker, Gothic akrs), from PIE *agro- "field" (cf. Latin ager "field, land," Greek agros, Sanskrit ajras "plain, open country").
Originally in English without reference to dimension; in late Old English the amount of land a yoke of oxen could plow in a day, afterward defined by statute as a piece 40 poles by 4, or an equivalent shape (5 Edw. I, 31 Edw. III, 24 Hen. VIII). Original sense retained in God's acre "churchyard."
is the translation of a word (tse'med), which properly means a yoke, and denotes a space of ground that may be ploughed by a yoke of oxen in a day. It is about an acre of our measure (Isa. 5:10; 1 Sam. 14:14).