ca·chet 
(kă-shā)
(kă-shā)n.
1.
a. Great prestige or appeal: a designer label with cachet.
b. A quality of prestige or appeal: "Federal courts have a certain cachet which state courts lack" (Christian Science Monitor).
c. A mark, as of distinction, individuality, or authenticity: "In our times the thick wad of credit cards is a cachet of respectability" (John D. MacDonald).
2. A seal on a document, such as a letter.
3.
a. A commemorative design stamped on an envelope to mark a postal or philatelic event.
b. A motto forming part of a postal cancellation.
4. A kind of wafer capsule formerly used by pharmacists for presenting an unpleasant-tasting drug.
[French cachet, seal, stamp of authenticity, distinctive character, from Middle French, seal : cacher, to press, squeeze (from Occitan cachar, from Old Provençal, from Latin coāctāre, to constrain; see CACHE) + -et, diminutive suffix (from Old French; see -ET). Sense 4, from French, from the resemblance of the wafer to a wax seal on a document.]