Meaning

noun a person or thing equal to another in value or measure or force or effect or significance etc

noun the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen

adjective being essentially equal to something

originFrom Latin aequivalentem, accusative singular of aequivalēns, present active participle of aequivaleō (“to be equivalent, have equal power”). By surface analysis, equi- + -valent. Mostly displaced native Middle English efenmete (See evenmete).

Etymology from Wiktionary, CC BY-SA 3.0