Etymology
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defoliant (n.)

"chemical used to defoliate," 1943; see defoliate + -ant. Defoliator (1875) was used of insects which destroy the leaves of trees.

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Antaeus 
Libyan giant slain by Herakles, from Latinized form of Greek Antaios, literally "opposite, opposed to, hostile," from anta "over against, face to face," related to anti "opposite, against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before").
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antsy (adj.)
"restlessly impatient," 1838, American English, from plural of ant + -y (2); probably reflecting the same image as the slang expression have ants in (one's) pants "be restless and fidgety" from a century later. Related: Antsiness.
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ante (n.)
in the game of poker, "stake of money placed in a pool by each player before drawing cards," 1838, American English poker slang, apparently from Latin ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before"). From 1846 as a verb.
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decongestant (n.)

"a decongestive agent," by 1950; see de- + congest + -ant. Related: Decongestion (1901); decongest (v.), by 1912; decongestive (adj.), by 1922.

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ante meridiem 
"of morning, before mid-day," 1560s, Latin, literally "before noon," from ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + accusative of meridies "midday, noon" (see meridian). Adjective antemeridian is attested from 1650s.
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reliant (adj.)

1856, "having or indicating reliance or confidence;" see rely (v.) + -ant. Perhaps based on reliance. Because its meaning shades into "dependent (on)," a sense attested by 1878, it would seem an odd name for an automobile, but Chrysler (Plymouth) nonetheless chose it as one in 1981.

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ambi- 
word-forming element meaning "both, on both sides," from Latin ambi- "around, round about" (before vowels amb-, also sometimes reduced to am-, an-), from PIE root *ambhi- "around," which is probably an ablative plural (*ant-bhi "from both sides") of *ant- "front, forehead."
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hydrant (n.)
"apparatus for drawing water from a street main," 1806, from Greek hydr-, stem of hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet") + -ant. OED double-damns it as "Irregularly formed" and "of U.S. origin."
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antediluvian (adj.)
"before Noah's flood," 1640s, from Latin ante "before" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + diluvium "a flood" (see deluge (n.)). Hence (humorously or disparagingly) "very antiquated" (1726). Coined by English physician Sir Thomas Browne (1605-1682). As a noun meaning "person who lived before the Flood," from 1680s. Related: antediluvial (1823).
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