stop-light (n.)

"brightness, radiant energy, that which makes things visible," Old English leht (Anglian), leoht (West Saxon), "light, daylight; spiritual illumination," from Proto-Germanic *leukhtam (source also of Old Saxon lioht, Old Frisian liacht, Middle Dutch lucht, Dutch licht, Old High German lioht, German Licht, Gothic liuhaþ "light"), from PIE root *leuk- "light, brightness."

The -gh- was an Anglo-French scribal attempt to render the Germanic hard -h- sound, which has since disappeared from this word.

The meaning "something used for igniting" is from 1680s. The sense of "a consideration which puts something in a certain view" (as in in light of) is from 1680s. As short for traffic light from 1938.

The figurative spiritual sense was in Old English; the sense of "mental illumination" is recorded by mid-15c. Quaker use is by 1650s; New Light/Old Light in church doctrine also is from 1650s.

Omnia, quae sunt, lumina sunt [Scotus Erigena (810?-877?) "All things that are, are light"]

The meaning "person eminent or conspicuous" is from 1590s. A source of joy or delight has been the light of (someone's) eyes since Old English:

Ðu eart dohtor min, minra eagna leoht [Juliana].

Phrases such as according to (one's) lights "to the best of one's natural or acquired capacities" preserve an older sense attested from 1520s. To figuratively stand in (someone's) light is from late 14c. To see the light "come into the world" is from 1680s; later as "come to full realization" (1812). The rock concert light-show is from 1966. To be out like a light "suddenly or completely unconscious" is from 1934.

late 14c., "a plug;" mid-15c., "a cessation" from motion or action, from stop (v.). Of mechanisms of musical instruments for stopping a hole and changing the tone, from c. 1500. Especially in reference to organs, "a set of pipes producing the same sound," presumably in reference to the knob activating them. Opening one swells the sound, hence figurative phrase pull out the stops "make every possible effort" (1909).

By 1560s as "a pause in speaking;" by 1590 as "mark to indicate a pause or stop in reading, a punctuation mark." The end of a sentence was a full stop, hence in punctuation "period," which, shortened to stop, was regularly printed in telegram messages at the end of sentences by 1936.

By 1500 as a kind of thrust in fencing. From 1660s in phonetics, "alphabetic sound involving complete closure of the mouth-organs." By 1831 in photography. The meaning "a stopping place" is from 1889.

Stop-sign, indicating traffic should stop, is by 1918. To put a stop to some activity "cause to cease, temporarily or permanently" is from 1670s (earlier give a stop to, 1580s).