The act of stopping, or the state of being stopped; hindrance of progress or of action; cessation; repression; interruption; check; obstruction. It is doubtful . . . whether it contributed anything to the stop of the infection. De Foe. Occult qualities put a stop to the improvement of natural philosophy. Sir I. Newton. It is a great step toward the mastery of our desires to give this stop to them. Locke. That which stops, impedes, or obstructs; as obstacle; an impediment; an obstruction. A fatal stop traversed their headlong course. Daniel. So melancholy a prospect should inspire us with zeal to oppose some stop to the rising torrent. Rogers. A device, or piece, as a pin, block, pawl, etc., for arresting or limiting motion, or for determining the position to which another part shall be brought. The closing of an aperture in the air passage, or pressure of the finger upon the string, of an instrument of music, so as to modify the tone; hence, any contrivance by which the sounds of a musical instrument are regulated. The organ sound a time survives the stop. Daniel. In the organ, one of the knobs or handles at each side of the organist, by which he can draw on or shut off any register or row of pipes; the register itself; as, the vox humana stop. A member, plain or molded, formed of a separate piece and fixed to a jamb, against which a door or window shuts. This takes the place, or answers the purpose, of a rebate. Also, a pin or block to prevent a drawer from sliding too far. A point or mark in writing or printing intended to distinguish the sentences, parts of a sentence, or clauses; a mark of punctuation. See Punctuation. The diaphragm used in optical instruments to cut off the marginal portions of a beam of light passing through lenses. The depression in the face of a dog between the skull and the nasal bones. It is conspicuous in the bulldog, pug, and some other breeds. Some part of the articulating organs, as the lips, or the tongue and palate, closed (a) so as to cut off the passage of breath or voice through the mouth and the nose (distinguished as a lip-stop, or a front-stop, etc., as in p, t, d, etc.), or (b) so as to obstruct, but not entirely cut off, the passage, as in l, n, etc.; also, any of the consonants so formed. H. Sweet. Stop bead (Arch.), the molding screwed to the inner side of a window frame, on the face of the pulley stile, completing the groove in which the inner sash is to slide. -- Stop motion (Mach.), an automatic device for arresting the motion of a machine, as when a certain operation is completed, or when an imperfection occurs in its performance or product, or in the material which is supplied to it, etc. -- Stop plank, one of a set of planks employed to form a sort of dam in some hydraulic works. -- Stop valve, a valve that can be closed or opened at will, as by hand, for preventing or regulating flow, as of a liquid in a pipe; -- in distinction from a valve which is operated by the action of the fluid it restrains. -- Stop watch, a watch the hands of which can be stopped in order to tell exactly the time that has passed, as in timing a race. See Independent seconds watch, under Independent, a.