Etymology
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invisible (adj.)
mid-14c., "not perceptible to sight, incapable of being seen," from Old French invisible (13c.), from Latin invisibilis "unseen, not visible," from in- "not" (see in- (1)) + visibilis (see visible). Meaning "kept out of sight" is from 1640s. As a noun, "things invisible," from 1640s. Invisible Man is from H.G. Wells's novel (1897); invisible ink is from 1680s. Related: Invisibly.
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invisibility (n.)
1560s, from Late Latin invisibilitas, from Latin invisibilis "not visible, unseen" (see invisible).
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leaven (v.)
"excite fermentation in," c. 1400, leueyn, from leaven (n.). Figurative sense "work upon by invisible or powerful influence" is from 1540s. Related: Leavened; leavening.
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antichthon (n.)

c. 1600, antichthones (plural), from Latin antichthontes, from Greek antikhthontes "people of the opposite hemisphere," from anti "opposite" (see anti-) + khthōn "land, earth, soil" (from PIE root *dhghem- "earth"). In Pythagorean philosophy, an imagined invisible double of earth.

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inconspicuous (adj.)
1620s, "invisible," from Late Latin inconspicuus "not conspicuous," from in- "not, opposite of, without" (see in- (1)) + Latin conspicuus (see conspicuous). Weakened sense of "not readily seen or noticed" developed by 1828. Related: Inconspicuously; inconspicuousness.
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unsightly (adj.)
1540s, "displeasing to the eye," from un- (1) "not" + sight (n.) + -ly (1). Similar formation in Middle Dutch onsichtlijc "invisible; ugly," Middle High German unsihtlih "invisible." Related: Unsightliness.

Middle English sightlie is attested from mid-15c. but only in the sense "visible;" unsightly is attested in Middle English only as an adverb meaning "invisibly" (late 15c.). Sightly as "pleasing to the eye" is from 1560s. Middle English also had unsighty "difficult or displeasing to look at" (early 15c., from sighty "attractive," late 14c.), also unsightily in the same sense (c. 1400).
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undermine (v.)

c. 1300, undermyne, "render unstable by digging at the foundation," from under + mine (v.1) "dig." The figurative sense "injure by invisible, secret, or dishonorable means" is attested from early 15c. Similar formation in Dutch ondermijnen, Danish underminere, German unterminiren. The Old English verb was underdelfan. Related: Undermined; undermining.

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perspiration (n.)

1610s, "a breathing through," a sense now obsolete, from French perspiration (1560s), noun of action from perspirer "perspire," from Latin perspirare "blow or breathe constantly," from per "through" (from PIE root *per- (1) "forward," hence "through") + spirare "to breathe, blow" (see spirit (n.)). Applied by 1620s to "excretion of invisible moistures through the skin," hence its later use as a euphemism for "sweat" (1725).

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blight (n.)
1610s, origin obscure; according to OED it emerged into literary speech from the talk of gardeners and farmers. It is perhaps from Old English blæce, blæcðu, a scrofulous skin condition and/or from Old Norse blikna "become pale" (from the group including bleach, bleak, etc.). Used in a general way of agricultural diseases, sometimes with suggestion of "invisible baleful influence;" hence figurative sense of "anything which withers hopes or prospects or checks prosperity" (1660s). Compare slang blighter. Urban blight "condition of disrepair and poverty in a previously thriving part of a city" attested by 1935.
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voice (n.)

late 13c., "sound made by the human mouth," from Old French voiz "voice, speech; word, saying, rumor, report" (Modern French voix), from Latin vocem (nominative vox) "voice, sound, utterance, cry, call, speech, sentence, language, word" (source also of Italian voce, Spanish voz), related to vocare "to call" (from PIE root *wekw- "to speak").

Replaced Old English stefn "voice," from Proto-Germanic *stemno, from PIE *stomen- (see stoma). Meaning "ability in a singer" is first attested c. 1600. Meaning "expression of feeling, etc." (in reference to groups of people, etc., such as Voice of America) is recorded from late 14c. Meaning "invisible spirit or force that directs or suggests," (especially in the context of insanity, as in hear voices in (one's) head, is from 1911.

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