Webster's Revised Unabridged Dictionary · 1913

Under

Under (un"dẽr) , preposition

[Anglo-Saxon under, prep. & adv.; akin to OFries. under, Old Saxon undar, Dutch onder, German unter, Old High German untar, Icelandic undir, Swedish & Danish under, Gothic undar, Latin infra below, inferior lower, Sanskrit adhas below. r201. Compare Inferior.]

1.
Below or lower, in place or position, with the idea of being covered; lower than; beneath; -- opposed to over; as, he stood under a tree; the carriage is under cover; a cellar extends under the whole house.
Fruit put in bottles, and the bottles let down into wells under water, will keep long. — Bacon
Be gathered now, ye waters under heaven, Into one place. — Milton
(a)
Denoting relation to some thing or person that is superior, weighs upon, oppresses, bows down, governs, directs, influences powerfully, or the like, in a relation of subjection, subordination, obligation, liability, or the like; as, to travel under a heavy load; to live under extreme oppression; to have fortitude under the evils of life; to have patience under pain, or under misfortunes; to behave like a Christian under reproaches and injuries; under the pains and penalties of the law; the condition under which one enters upon an office; under the necessity of obeying the laws; under vows of chastity.
Both Jews and Gentiles... are all under sin. — Rom. iii. 9
That led the embattled seraphim to war Under thy conduct. — Milton
Who have their provand Only for bearing burdens, and sore blows For sinking under them. — Shakespeare
(b)
Denoting relation to something that exceeds in rank or degree, in number, size, weight, age, or the like; in a relation of the less to the greater, of inferiority, or of falling short.
Three sons he dying left under age. — Spenser
Medicines take effect sometimes under, and sometimes above, the natural proportion of their virtue. — Hooker
There are several hundred parishes in England under twenty pounds a year. — Swift
It was too great an honor for any man under a duke. — Addison
Several young men could never leave the pulpit under half a dozen conceits. — Swift

Hence, it sometimes means at, with, or for, less than; as, he would not sell the horse under sixty dollars.

(c)
Denoting relation to something that comprehends or includes, that represents or designates, that furnishes a cover, pretext, pretense, or the like; as, he betrayed him under the guise of friendship; Morpheus is represented under the figure of a boy asleep.
A crew who, under names of old renown... abused Fanatic Egypt. — Milton
Mr. Duke may be mentioned under the double capacity of a poet and a divine. — Felton
Under this head may come in the several contests and wars betwixt popes and the secular princes. — C. Leslie
(d)
Less specifically, denoting the relation of being subject, of undergoing regard, treatment, or the like; as, a bill under discussion.
Abject and lost, lay these, covering the flood, Under amazement of their hideous change. — Milton
Collocations (13)
Under arms (Military) , (a) Drawn up fully armed and equipped. (b) Enrolled for military service; as, the state has a million men under arms.
Under canvas (Nautical) , Moved or propelled by sails; -- said of any vessel with her sail set, but especially of a steamer using her sails only, as distinguished from one under steam. Under steam and canvas signifies that a vessel is using both means of propulsion. Provided with, or sheltered in, tents.
Under fire , exposed to an enemy's fire; taking part in a battle or general engagement.
Under foot , See under Foot, n.
Under ground , below the surface of the ground.
Under one's signature , with one's signature or name subscribed; attested or confirmed by one's signature. Compare the second Note under Over, prep.
Under sail (Nautical) , (a) With anchor up, and under the influence of sails; moved by sails; in motion. (b) With sails set, though the anchor is down. (c) Same as Under canvas (a), above. — Totten
Under sentence , having had one's sentence pronounced.
Under the breath or Under one's breath , with low voice; very softly.
Under the lee (Nautical) , to the leeward; as, under the lee of the land.
Under the gun , Under psychological pressure, such as the need to meet a pressing deadline; feeling pressured
Under water , below the surface of the water.
Under way or Under weigh (Nautical) , in a condition to make progress; having started.

Under (un"dẽr) , adverb

In a lower, subject, or subordinate condition; in subjection; -- used chiefly in a few idiomatic phrases; as, to bring under, to reduce to subjection; to subdue; to keep under, to keep in subjection; to control; to go under, to be unsuccessful; to fail; to go bankrupt.
I keep under my body, and bring it into subjection. — 1 Cor. ix. 27
The minstrel fell, but the foeman's chain Could not bring his proud soul under. — Moore

Under is often used in composition with a verb to indicate lowness or inferiority in position or degree, in the act named by the verb; as, to underline; to undermine; to underprop.

Under , adjective

Lower in position, intensity, rank, or degree; subject; subordinate; -- generally in composition with a noun, and written with or without the hyphen; as, an undercurrent; undertone; underdose; under-garment; underofficer; undersheriff.
Collocations (1)
Under covert (Zoology) , one of the feathers situated beneath the bases of the quills in the wings and tail of a bird. See Illust. under Bird.