underrun verb 3noun 2forms 3 verb3 •To run or pass under.He spoke fast, with the uneasy tone that so often underran his words. — 1904 •To pass along and under, e.g. a cable, for the purpose of taking it in or examining it. •To separate the parts of (a tackle) and put them in order. noun2 •A condition in which fewer products are delivered or produced than had been ordered. •A condition in which the read/write buffer is fed with data at a slower rate than required; a buffer underrun. formsunderran · underrunning · underruns