An Etymological Dictionary of Astronomy and Astrophysics

Equal in value, measure, force, effect, significance, etc.

Etymology (EN): From L.L. æquivalentem (nominative æquivalens) “equivalent,” p.p. of æquivalere “be equivalent,” from L. æquus, → equal + valere “to be worth; be strong.”

Etymology (PE): Hamug-arz, from hamug-, → equi-,

• arz stem of arzidan “to be worth,” arzân “worthy; of small value, cheap,” arj “esteem, honour, price, worth;” Mid.Pers. arz “value, worth,” arzidan “be worth,”
  arzân “valuable;” Av. arəjaiti “is worth,” arəja- “valuable,” arəg- “to be worth;” cf. Skt. arh- “to be worth, to earn,” árhant- “worthy person;” Gk. alphanein “to bring in as profit,” alphein “to ear, obtain;” Lith. algà “salary, pay;” PIE base *alg^wh- “to earn; price, value.”