stop-watch (n.)

Middle English stoppen, "obstruct (a passage) with a physical barrier; close up by filling, stuffing, or plugging," from Old English -stoppian (in forstoppian "to stop up, stifle"), a general West Germanic word, cognate with Old Saxon stuppon, West Frisian stopje, Middle Low German stoppen, Old High German stopfon, German stopfen "to plug, stop up," Old Low Frankish (be)stuppon "to stop (the ears)." Related: Stopped; stopping.

These words are said by many sources to be a Germanic borrowing of Vulgar Latin *stuppare "to stop or stuff with tow or oakum" (source of Italian stoppare, French étouper "to stop with tow"), from Latin stuppa "coarse part of flax, tow." In support of this theory, it is said that plugs made of tow were used from ancient times in the Rhine valley. Century Dictionary says this "suits phonetically," but "is on grounds of meaning somewhat doubtful." Barnhart, for one, proposes the whole Germanic group might be native, from a native base *stoppon.

Senses having to do with "bring or come to a halt; discontinue or cause to cease from a course or action" developed in 15c. in English (but have been adopted in other languages). They extend from the notion of "prevent a flow by blocking a hole," and in some cases the sense might have been influenced by Latin stupere "be stunned, be stupefied."

The transitive sense of "hinder from progress or procedure, put a stop to" (a thief, a clock, conception) is by late 14c., as is that of "hold (someone or something) back from a specified course or purpose." By c. 1400 stop could mean "shut (someone in something), confine, shut away from." By 1400 stop also was used as "prevent the continuance of" and by 1520s intransitively as "cease from forward motion, come to a stand."

The transitive meaning "leave off, desist" is by 1520s; the intransitive meaning "check oneself" is 1680s. Of travelers, "make a halt or stay, tarry," by 1711. Of immaterial things, "discontinue, cease, come to an end," by 1733. In reference to the ears "to plug or cover," early 14c.

Middle English wacche, from Old English wæcce "a watching, state of being or remaining awake, wakefulness;" also "act or practice of refraining from sleep for devotional or penitential purposes;" from wæccan "keep watch, be awake," from Proto-Germanic *wakjan, from PIE root *weg- "to be strong, be lively."

The meaning "small timepiece" is from 1580s, developing from that of "a clock to wake up sleepers" (mid-15c.).

From c. 1200 as "one of the periods into which the night is divided," in reference to ancient times translating Latin vigilia, Greek phylakē, Hebrew ashmoreth. From mid-13c. as "a shift of guard duty; an assignment as municipal watchman;" late 13c. as "person or group obligated to patrol a town (especially at night) to keep order, etc."

Also in Middle English, "the practice of remaining awake at night for purposes of debauchery and dissipation;" hence wacches of wodnesse "late-night revels and debauchery."

The alliterative combination watch-and-ward for the old custom of keeping order in cities and towns preserves the distinction of watch for night-time municipal patrols and ward (n.) for guarding by day; in combination, they mean "continuous vigilance."

The military sense of "military guard, sentinel" is from late 14c. Also in early 18c. as a designation of certain irregular troops in the Scottish Highlands.

The general sense of "careful observation, watchfulness, vigilance" is from late 14c.; to keep watch is from late 14c. The meaning "period of time in which a division of a ship's crew remains on deck" is from 1580s.

The Hebrews divided the night into three watches, the Greeks usually into four (sometimes five), the Romans (followed by the Jews in New Testament times) into four. [OED]

On þis niht beð fowuer niht wecches: Biforen euen þe bilimpeð to children; Mid-niht ðe bilimpeð to frumberdlinges; hanecrau þe bilimpeð þowuene men; morgewile to alde men. [Trinity Homilies, c. 1200]