An Etymological Dictionary of Astronomy and Astrophysics

1. A real thing.
   

2. Being or existence, especially when considered as independent, separate, or self-contained.
   

3. Computer science: Something about which data is recorded. Entities have → attributes.

Etymology (EN): From L.L. entitatem, from L.L. ens (genitive entis) “being, thing,” from esse “to be,” cognate with Pers. hast, ast, as below.

Etymology (PE): Hastâr, from hast (noun), as in hast-o-nist, or contraction of hasti “existence,” from hastan “to be” (variant astan, ast “is;” Mid.Pers. (h)ast “is,” (h)astih “existence;” O.Pers. ah- “to be,” astiy “is;”
Av. ah- “to be” (ahmī, ahī, astī); cf. Skt. as- “to be,” ásti “is;” Gk. esti “is;” L. est “is;” Russ. yest “is;” Goth. ist; E. is), + suffix -âr (as in padidâr). Alternatively, from hast (noun), as above, + -âr contraction of -dâr (as in dustâr) present stem of dâštan “to have, to possess” (Mid.Pers. dâštan, O.Pers./Av. root dar- “to hold, keep back, maintain, keep in mind,” Skt. dhr-, dharma- “law,”
Gk. thronos “elevated seat, throne,” L. firmus “firm, stable,” Lith. daryti “to make,” PIE *dher- “to hold, support”).