Old English under (prep.) "beneath, among, before, in the presence of, in subjection to, under the rule of, by means of," also, as an adverb, "beneath, below, underneath," expressing position with reference to that which is above, from Proto-Germanic *under- (source also of Old Frisian under, Dutch onder, Old High German untar, German unter, Old Norse undir, Gothic undar), from PIE *ndher- "under" (source also of Sanskrit adhah "below;" Avestan athara- "lower;" Latin infernus "lower," infra "below").
Productive as a prefix in Old English, as in German and Scandinavian (often forming words modeled on Latin ones in sub-). Notion of "inferior in rank, position, etc." was present in Old English. With reference to standards, "less than in age, price, value," etc., late 14c. As an adjective, "lower in position; lower in rank or degree" from 13c. Also used in Old English as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand).
Under the weather "indisposed" is from 1810. Under the table is from 1913 in the sense of "very drunk," 1940s in sense of "illegal" (under-board "dishonest" is from c. 1600). To keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1540s; to speak under (one's) breath "in a low voice" is attested from 1832.
pass v.
late 13c., passen (transitive), "to go by (something)," also "to cross over," from Old French passer "to pass" (11c.), from Vulgar Latin *passare "to step, walk, pass" (source also of Spanish pasar, Italian passare), from Latin passus "step, pace" (from PIE root *pete- "to spread").
Intransitive sense of "to go on, to move forward, make one's way" is attested from c. 1300. The figurative sense of "to experience, undergo" (as in pass the time) is recorded from late 14c. Sense of "to go through an examination successfully" is from early 15c. Meaning "decline to do something" is attested from 1869, originally in cards (euchre). In football, hockey, soccer, etc., the meaning "to transfer the ball or puck to another player" is from c. 1865. Related: Passed; passing.
The meaning "to be thought to be something one is not" (especially in a racial sense) is from 1935, from pass oneself off(as), which is attested by 1809. The general verb sense of "to be accepted as equivalent" is from 1590s. Pass up "decline, refuse" is attested from 1896. Pass the buck is from 1865, said to be poker slang reference to the buck horn-handled knife that was passed around to signify whose turn it was to deal. Pass the hat "seek contributions" is from 1762. Pass-fail as a grading method is attested from 1955, American English.