(US) Initialism of formerly restricted data: a classification level below RD that allows sharing among military agencies.

(physics) a surface having many closely spaced lines or slits; used to produce optical spectra by mutual interference

(mineralogy) A pyroxene mineral, a sodium aluminium silicate with the chemical formula Na(Al,Fe³⁺)Si₂O₆, found in metamorphic rocks.

(transitive) To characterize as a pathology or disease; to characterize (a person) as suffering from a disease.