An Etymological Dictionary of Astronomy and Astrophysics

1. (v.tr.) To make indistinct and hazy in outline or appearance.
   
2. (v.intr.) To become indistinct.

Etymology (EN): Probably akin to M.E. bleren “to blear.”

Etymology (PE): Târ “dark, obscure, cloudy” Mid.Pers. târ, from Mid./Mod.Pers. târ “dark, obscure, cloudy.”