An Etymological Dictionary of Astronomy and Astrophysics

1. To bring to a certain state, condition, arrangement, etc.
   Math.: To change the denomination or form, but not the value, of (a fraction, polynomial, etc.).
   Chem.: To add an electron to.
   
2. To bring down to a smaller extent, size, amount, number, etc.; synonymous with
   → decrease.

Etymology (EN): M.E. reducen “to lead back,” from
O.Fr. reducer, from L. reducere, from → re- “back” + ducere “to bring, to lead.”

Etymology (PE): From bâz-, → re- + Mid.Pers. hâxtan, hâzidan “to lead, guide, persuade,” Av. hak-, hacaiti “to attach oneself to, to join,” cf. Skt. sacate “accompanies, follows,” Gk. hepesthai “to follow,” L. sequi “to follow;” PIE *sekw- “to follow.”
Kâstan, → decrease.