An Etymological Dictionary of Astronomy and Astrophysics

1a) Lacking in light or illumination; dark; dim; murky.

1b) Indistinct to the sight or any other sense.

1c) Not clear to the understanding.

2. To make dark, dim, indistinct, etc.

Etymology (EN): From O.Fr. obscur “dark, dim, not clear,” from L. obscurus “covered over, dark, obscure,” from ob “over” + -scurus “covered,” from PIE *(s)keu- “to cover, conceal;” from which derives also the term → sky.

Etymology (PE): Tiré, from Mid.Pers. târag “dark, turbid,” related to târik “dark,” Mid.Pers. târig “dark,” târ “darkness,” Av. taθra- “darkness,” taθrya- “dark,” cf. Skt. támisrâ- “darkness, dark night,” L. tenebrae “darkness,” Hittite taš(u)uant- “blind,” O.H.G. demar “twilight.”
Tiré kardan compound verb with kardan “to do,” → -ize.