An Etymological Dictionary of Astronomy and Astrophysics

1. (v.tr.) To cause to diminish, to make less. (v.intr.) To diminish or lessen in extent, quantity, power, etc.
   

2. The act or process of decreasing; condition of being decreased. → Forbush decrease.

Etymology (EN): Decrease, from M.E. decres (n.), decresen, from
O.Fr. descreistre, from L. decrescere, from → de- + crescere “to grow,” → crescent.

Etymology (PE): Kâstan, kâh-, from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen,” Av. kasu- “small, little” (Mod.Pers. keh), Proto-Iranian *kas- “to be small, diminish, lessen;” kâheš verbal noun from kâhidan.