adjective

1. equal in quantity, value, force, meaning, etc.
2. Chem. having the same valence
3. Geom. equal in area, volume, etc., but not of the same shape

Etymology: ME < OFr < LL aequivalens, prp. of aequivalere, to have equal power: see equi- & value

noun

1. an equivalent thing
2. Chem.
   1. the quantity by weight (of a substance) that combines with 8 grams of oxygen or 1.008 grams of hydrogen
   2. the weight obtained by dividing the atomic weight by the valence