Synonyms for Under:

adj.

all (adjective)
nether.
inferior (adjective)
below, dependent, inferior, junior, lesser, second, subject, subordinate, subservient, underling.
less (adjective)
beneath, less, lower than, below.
lower (adjective)
lower.
subordinate (adjective)
bound, compliant, constrained, deferent, enslaved, enthralled, obedient, servile, subjugated, submissive, supine, Subjected, unfranchised, dependent, junior, subject, subordinate, subservient.

adv

under (adverb)
below, beneath, underneath, lower than.

adv.

below (adverb)
beneath, down, downward, inferior, lower, nether, supporting, underneath.
secondary (adverb)
dependent, following, junior, lesser, low, obedient, subject, subjugated, subordinate, subservient.
under (adverb)
underneath.

n.

above, academic, advanced, applied, curricular, diachronic, didactic, educational, elementary, formal, graduate, over, supporting. apart, by, depending on, different, following, strictly speaking, according to, in accordance with, in the eyes of the law/world etc., on a case-by-case basis, on (someone's/something's) merit. after, assignment, big, deficient, excess, inadequate, initial, insufficient, nameless, namesake, nee, scarce, short, shy, wanting, Of, naming ceremony. age, age bracket, aged, at, contemporary, lower, minor, minor league, old, peer, petty, secondary, small, subaltern, smalltime, age gap. ascending, bouncy, down, downward, skyward, up, upward. asleep, comatose, fast asleep, out, semiconscious, sound asleep, unconscious, out cold, out for the count. subterranean, underfoot, underground, underlying, underwater. clothed, crusted, encrusted, thickly, thinly, Caked, be tipped with something. astrology (noun)
aquarius, aries, astrologer, astrological, astrology, cancer, capricorn, cast, chart, gemini.
inferior (noun)
nether.
under (noun)
below, low, low-level, nether, subordinate.

prep.

inferior (preposition)
beneath.
lower (preposition)
below.

Other synonyms:

age bracket, aged, ascending, comatose, crusted, downward, encrusted, semiconscious, skyward, subterranean, underlying, Caked, smalltime, according to, age gap. age, asleep, bouncy, clothed, down, inadequate, insufficient, minor, minor league, old, scarce, secondary, subaltern, thinly. contemporary, deficient, peer, shy. lower, thickly, unconscious. at, by, petty, small. wanting. short. out. beneath
underfoot.
submarine
underwater.
subterranean
underground.
Other relevant words:
after, ascending, comatose, deficient, down, downward, following, inadequate, insufficient, low, low-level, lower, minor, minor league, nether, peer, petty, scarce, secondary, short, shy, skyward, small, subaltern, subterranean, supporting, thickly, unconscious, underfoot, underground, underlying, underwater, up, upward, wanting, Caked, Of, smalltime, according to, out cold, in accordance with.

Usage examples for under

  1. " She's gettin' under way, like enough. – Uncle William The Man Who Was Shif'less by Jennette Lee
  2. Under your bed, where they belong. – Gaslight Sonatas by Fannie Hurst