1845, "drawers for men" (derogatory), diminutive of pants with -ie. The meaning "underpants for women or girls" is recorded by 1908. The college prank panty raid is attested from 1952.
Entries linking to panties
pants n.
"trousers, drawers," 1840, see pantaloons. The word was limited to vulgar and commercial use at first.
I leave the broadcloth,—coats and all the rest,—
The dangerous waistcoat, called by cockneys "vest,"
The things named "pants" in certain documents,
A word not made for gentlemen, but "gents";
[Oliver Wendell Holmes, "Urania: A Rhymed Lesson," 1846]
Colloquial singular pant is attested from 1893. To wear the pants "be the dominant member of a household" is by 1931. To do something by the seat of (one's) pants "by human instinct" is from 1942, originally of pilots, perhaps with some notion of being able to sense the condition and situation of the plane by engine vibrations, etc. To be caught with (one's) pants down "discovered in an embarrassing condition" is from 1932.
-ie
alternative spelling of -y; now mostly of -y (3), but formerly of the others as well.