entity (n.)

1590s, "being," from Late Latin entitatem (nominative entitas), from ens (genitive entis) "a thing," proposed by Caesar as present participle of esse "be" (see is), to render Greek philosophical term to on "that which is" (from neuter of present participle of einai "to be," from PIE root *es- "to be"). Originally abstract; concrete sense in English is from 1620s.