[rey-zohn de-truh; Fr. re-zawn de-truh ] 
[rey-zohnz de-truh; Fr. re-zawn de-truh ] . | reason or justification for being or existence: Art is the artist's raison d'être. |
| rai·son d'ê·tre (rā'zōn dět'rə, rě-zôɴ) n. pl. rai·sons d'être (rā'zōn, rě-zôɴ) Reason or justification for existing. [French : raison, reason + de, of, for + être, to be.] |
A basic, essential purpose; a reason to exist: “Professor Naylor argues that in the nuclear age, infantry forces have lost their raison d'être.” From French, meaning “reason for being.”