Bifilar \Bi*fi"lar\, a. [Pref. bi- + filar.] Two-threaded; involving the use of two threads; as, bifilar suspension; a bifilar balance. {Bifilar micrometer} (often called {a bifilar}), an instrument form measuring minute distances or angles by means of two very minute threads (usually spider lines), one of which, at least, is movable; -- more commonly called a {filar micrometer}.