noun
(accounting) A condition in which fewer products are delivered or produced than had been ordered.
(computing) A condition in which the read/write buffer is fed with data at a slower rate than required; a buffer underrun.
verb
To run or pass under.
(nautical) To pass along and under, e.g. a cable, for the purpose of taking it in or examining it.
(nautical) To separate the parts of (a tackle) and put them in order.