fə̇ˈnan(t)thrəˌlēn, -_lə̇n noun
( -s )
Etymology: International Scientific Vocabulary phenanthr- + quin oline
: any of three crystalline nitrogen bases C 12 H 8 N 2 related to phenanthrene and derivable from ortho-, meta-, and para -phenylenediamine; di-aza-phenanthrene ; especially : the ortho or 1,10-isomer that forms a red coordination complex with ferrous ions useful as an oxidation-reduction indicator (as with potassium permanganate as oxidizing agent) because it becomes faint blue in the oxidized form