Etymology
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vitreous (adj.)
early 15c., "glasslike," from Latin vitreus "of glass, glassy," from vitrum "glass," which perhaps was so called for its color (compare vitrium "woad"). Vitreous humor attested from 1660s.
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vitrine (n.)
"glass show-case," 1880, from French vitrine, from vitre "glass, window-glass," from Latin vitrum "glass" (see vitreous).
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in vitro 
1892, scientific Latin; "in a test tube, culture dish, etc.;" literally "in glass," from Latin vitrum "glass" (see vitreous).
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vitro- 
word-forming element meaning "glass," from combining form of Latin vitrum "glass" (see vitreous).
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vitrify (v.)

1590s, from French vitrifier (16c.), from Latin vitrum "glass" (see vitreous) + -ficare, combining form of facere "to make" (from PIE root *dhe- "to set, put"). Related: Vitrified; vitrification.

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vitriol (n.)
late 14c., "sulphate of iron," from Old French vitriol (13c.), from Medieval Latin vitriolum "vitriol," noun use of neuter of vitriolus, variant of Late Latin vitreolus "of glass," from Latin vitreus "of glass, glassy," from vitrum "glass" (see vitreous). So called from its glassy appearance in certain states. Meaning "bitter or caustic feelings" first attested 1769, in reference to the corrosive properties of vitriol (when heated it produces sulfuric acid, formerly called oil of vitriol).
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woad (n.)

Old English wad "woad," also the blue dye made from its leaves, from Proto-Germanic *waidīn (source also of Danish vaid, Old Frisian wed, Middle Dutch wede, Dutch wede, Old High German weit, German Waid "woad"), which is perhaps cognate with Latin vitrium "glass" (see vitreous), but Boutkan considers it a substratum word. Formerly much cultivated; since superseded by indigo. French guède, Italian guado are Germanic loan-words.

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positive (adj.)

early 14c., originally a legal term meaning "formally laid down, decreed or legislated by authority" (opposed to natural),  from Old French positif (13c.) and directly from Latin positivus "settled by agreement, positive" (opposed to naturalis "natural"), from positus, past participle of ponere "put, place" (see position (n.)).

The sense of "absolute" is from mid-15c. Meaning in philosophy of "dealing only with facts" is from 1590s. Sense broadened to "expressed without qualification" (1590s), then, of persons, "confident in opinion" (1660s). The meaning "possessing definite characters of its own" is by 1610s. The mathematical use for "greater than zero" is by 1704. Psychological sense of "concentrating on what is constructive and good" is recorded from 1916. Positive thinking is attested from 1953. The sense in electricity is from 1755.  

There are probably no two bodies differing in nature which are not capable of exhibiting electrical phaenomena, either by contact, pressure, or friction ; but the first substances in which the property was observed, were vitreous and resinous bodies ; and hence the different states were called states of resinous and vitreous electricity ; and resinous bodies bear the same relation to flint glass, as silk. The terms, negative and positive electricity, have been likewise adopted, on the idea, that the phaenomena depend upon a peculiar subtile fluid, which becomes in excess in the vitreous, and deficient in the resinous bodies ; and which is conceived by its motion and transfer, to produce the electrical phaenomena. [Sir Humphry Davy, "Elements of Chemical Philosophy," London, 1812]
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